biblatex-apa: Multiple citations in the same parentheses with the same first author, but different co-authors get condensed

Question

@MISC{john_big_1991,
  author = {John, Oliver P. and Donahue, E. M. and Kentle, R. L.},
  title = {The Big Five Inventory--Versions 4a and 54},
  date = {1991},
  langid = {american},
  publisher = {Berkeley, {CA:} University of California, Berkeley, Institute of
    Personality and Social Research}
}

@INCOLLECTION{john_paradigm_2008,
  author = {John, Oliver P. and Naumann, Laura P. and Soto, Christopher J.},
  editor = {John, Oliver P. and Robins, Richard W. and Pervin, Lawrence A.},
  title = {Paradigm Shift to the Integrative Big Five Trait Taxonomy: History,
    Measurement, and Conceptual Issues},
  booktitle = {Handbook of personality: theory and research},
  date = {2008},
  edition = {3},
  publisher = {Guilford Press},
  location = {New York},
  isbn = {9781593858360},
  pages = {114-158},
  langid = {american}
}

These two BibLaTeX entries cited within the same parentheses with...

\parencite{john_big_1991, john_paradigm_2008}

...lead to the following citation output:

(John, Donahue & Kentle, 1991, 2008)

As the co-authors clearly aren't the same although the first author is, I guess this shouldn't happen.

My Babel and BibLaTeX settings are as follows:

\usepackage[american,ngerman]{babel}
\usepackage[
    style=apa,
    sortcites=true,
    sorting=nyt,
    backend=biber,
    autolang=other
    ]{biblatex}
\DeclareLanguageMapping{ngerman}{ngerman-apa} % for language switching
\DeclareLanguageMapping{american}{american-apa} % for language switching

I also suppress some fields like url and redefine some bibliography strings, but I assume that this shouldn't be the root of the reported problem.

Also, if I inverse the citation...

\parencite{john_paradigm_2008, john_big_1991}

...and deactivate sorting, my output will be:

(John, Naumann & Soto, 2008, 1991)

Is there any BibLaTeX setting I've missed that fixes this problem or is this the expected behavior?

---

EDIT: I'd expect the first multiple citation to look like this:

(John, Donahue & Kentle, 1991; John, Naumann & Soto, 2008)

I really got no idea of how potential subsequent multiple citations with the same references should look like. The following would at least seem odd, as stated by moewe in his answer below:

(John et al., 1991; John et al., 2008)

Answer 1

As explained in my comments above, this has to do with the way biblatex-apa has to handle subsequent citations.

In APA style, the first citation has to contain a full list of authors while subsequent citations have only a very short truncated label of usually the first author plus "et al.". This is implemented in apa.cbx by a very special labelname format, that labelname is however not printed at the first occurrence. This behaviour causes the displayed name and the namehash (which is based on labelname) to diverge in certain situations.

A fix is to change all the namehashes in apa.cbx to fullhash like so.

\makeatletter
\def\cbx@apa@ifnamesaved{%
  \xifinlist{\thefield{fullhash}}{\cbx@apa@names}
    {\@firstoftwo}
    {\@secondoftwo}}

\newbibmacro*{cite:author}{%
  \iffieldequals{fullhash}{\cbx@lasthash}
% Multiple cites in one command
   {\setunit{\compcitedelim}%
    \usebibmacro{cite:plabelyear+extrayear}}%
% Single cite
   {\ifthenelse{\ifnameundef{labelname}\OR\iffieldequalstr{entrytype}{patent}}
% No author/editor
     {\usebibmacro{cite:noname}%
       \savefield{fullhash}{\cbx@lasthash}}
% Normal cite
     {\ifnameundef{shortauthor}
        {\printnames[labelname][-\value{listtotal}]{labelname}}%
        {\cbx@apa@ifnamesaved
          {\printnames{shortauthor}}
          {\printnames[labelname][-\value{listtotal}]{author}\addspace\printnames[sabrackets]{shortauthor}}}%
      \savefield{fullhash}{\cbx@lasthash}}}%
   \setunit{\multicitedelim}}

\newbibmacro*{cite}{%
  \iffieldequals{fullhash}{\cbx@lasthash}
% Multiple cites in one command
   {\setunit{\compcitedelim}%
    \usebibmacro{cite:plabelyear+extrayear}}%
% Single cite
   {\ifthenelse{\ifnameundef{labelname}\OR\iffieldequalstr{entrytype}{patent}}
% No author/editor
     {\usebibmacro{cite:noname}%
       \setunit{\nameyeardelim}%
       \usebibmacro{cite:plabelyear+extrayear}%
       \savefield{fullhash}{\cbx@lasthash}}
% Normal cite
     {\ifnameundef{shortauthor}
        {\printnames[labelname][-\value{listtotal}]{labelname}}%
        {\cbx@apa@ifnamesaved
          {\printnames{shortauthor}}
          {\printnames[labelname][-\value{listtotal}]{author}\addspace\printnames[sabrackets]{shortauthor}}}%
      \setunit{\nameyeardelim}%
      \usebibmacro{cite:plabelyear+extrayear}%
      \savefield{fullhash}{\cbx@lasthash}}}%
   \setunit{\multicitedelim}}

\newbibmacro*{textcite}{%
  \iffieldequals{fullhash}{\cbx@lasthash}
% Compact cite - more than one thing for same author
    {\setunit{\compcitedelim}%
     \usebibmacro{cite:plabelyear+extrayear}}
% New cite
    {%
    \ifbool{cbx:parens}
      {\bibcloseparen\global\boolfalse{cbx:parens}}
      {}%
      \setunit{\compcitedelim}%
      \ifthenelse{\ifnameundef{labelname}\OR\iffieldequalstr{entrytype}{patent}}
  % No author/editor or patent
       {\iffieldundef{shorthand}%
    % Cite using title
         {\usebibmacro{cite:noname}%
          \setunit{\ifbool{cbx:np}%
                   {\nameyeardelim}%
                   {\global\booltrue{cbx:parens}\addspace\bibopenparen}}%
          \usebibmacro{cite:plabelyear+extrayear}}
    % Cite using shorthand
         {\usebibmacro{cite:shorthand}}}
  % Normal cite with author/editor
  % Normal full cite
       {\ifnameundef{shortauthor}%
    % Normal full cite
         {\printnames[labelname][-\value{listtotal}]{labelname}}
    % Cite using short author
         {\cbx@apa@ifnamesaved
           {\printnames{shortauthor}}
           {\printnames[labelname][-\value{listtotal}]{author}}}%
  % Year
        \setunit{\ifbool{cbx:np}
                  {\nameyeardelim}
                  {\global\booltrue{cbx:parens}\addspace\bibopenparen}}%
  % Put the shortauthor inside the year brackets if necessary
        \ifnameundef{shortauthor}
         {}
         {\cbx@apa@ifnamesaved
           {}
           {\printnames{shortauthor}\setunit{\nameyeardelim}}}%
  % Actual year printing
        \usebibmacro{cite:plabelyear+extrayear}%
  % Save name hash for checks later
        \savefield{fullhash}{\cbx@lasthash}}}}

\newbibmacro*{citeyear}{%
  \iffieldundef{labelyear}
    {\usebibmacro{cite:init}}
    {\iffieldequals{fullhash}{\cbx@lasthash}
       {\setunit{\compcitedelim}%
        \usebibmacro{cite:plabelyear+extrayear}}
       {\usebibmacro{cite:plabelyear+extrayear}%
        \savefield{fullhash}{\cbx@lasthash}}}%
  \setunit{\multicitedelim}}

\newbibmacro*{cite:post}{%
  \xifinlist{\thefield{fullhash}}{\cbx@apa@names}
    {}
    {\listxadd{\cbx@apa@names}{\thefield{fullhash}}}}
\makeatother

The MWE

\documentclass{scrartcl}
\usepackage{csquotes}
\usepackage[ngerman]{babel} 
\usepackage[style=apa, backend=biber]{biblatex}
\DeclareLanguageMapping{ngerman}{ngerman-apa} % for language switching
\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@MISC{john_big_1991,
  author = {John, Oliver P. and Donahue, E. M. and Kentle, R. L.},
  title = {The Big Five Inventory--Versions 4a and 54},
  date = {1991},
  langid = {american},
  publisher = {Berkeley, {CA:} University of California, Berkeley, Institute of
    Personality and Social Research}
}
@MISC{john_big_1992,
  author = {John, Oliver P. and Donahue, E. M. and Kentle, R. L.},
  title = {The Big Five Inventory--Versions 4b and 5},
  date = {1992},
  langid = {american},
  publisher = {Berkeley, {CA:} University of California, Berkeley, Institute of
    Personality and Social Research}
}

@INCOLLECTION{john_paradigm_2008,
  author = {John, Oliver P. and Naumann, Laura P. and Soto, Christopher J.},
  editor = {John, Oliver P. and Robins, Richard W. and Pervin, Lawrence A.},
  title = {Paradigm Shift to the Integrative Big Five Trait Taxonomy: History,
    Measurement, and Conceptual Issues},
  booktitle = {Handbook of personality: theory and research},
  date = {2008},
  edition = {3},
  publisher = {Guilford Press},
  location = {New York},
  isbn = {9781593858360},
  pages = {114-158},
  langid = {american}
}
\end{filecontents*}

\bibliography{\jobname.bib}

\makeatletter
\def\cbx@apa@ifnamesaved{%
  \xifinlist{\thefield{fullhash}}{\cbx@apa@names}
    {\@firstoftwo}
    {\@secondoftwo}}

\newbibmacro*{cite:author}{%
  \iffieldequals{fullhash}{\cbx@lasthash}
% Multiple cites in one command
   {\setunit{\compcitedelim}%
    \usebibmacro{cite:plabelyear+extrayear}}%
% Single cite
   {\ifthenelse{\ifnameundef{labelname}\OR\iffieldequalstr{entrytype}{patent}}
% No author/editor
     {\usebibmacro{cite:noname}%
       \savefield{fullhash}{\cbx@lasthash}}
% Normal cite
     {\ifnameundef{shortauthor}
        {\printnames[labelname][-\value{listtotal}]{labelname}}%
        {\cbx@apa@ifnamesaved
          {\printnames{shortauthor}}
          {\printnames[labelname][-\value{listtotal}]{author}\addspace\printnames[sabrackets]{shortauthor}}}%
      \savefield{fullhash}{\cbx@lasthash}}}%
   \setunit{\multicitedelim}}

\newbibmacro*{cite}{%
  \iffieldequals{fullhash}{\cbx@lasthash}
% Multiple cites in one command
   {\setunit{\compcitedelim}%
    \usebibmacro{cite:plabelyear+extrayear}}%
% Single cite
   {\ifthenelse{\ifnameundef{labelname}\OR\iffieldequalstr{entrytype}{patent}}
% No author/editor
     {\usebibmacro{cite:noname}%
       \setunit{\nameyeardelim}%
       \usebibmacro{cite:plabelyear+extrayear}%
       \savefield{fullhash}{\cbx@lasthash}}
% Normal cite
     {\ifnameundef{shortauthor}
        {\printnames[labelname][-\value{listtotal}]{labelname}}%
        {\cbx@apa@ifnamesaved
          {\printnames{shortauthor}}
          {\printnames[labelname][-\value{listtotal}]{author}\addspace\printnames[sabrackets]{shortauthor}}}%
      \setunit{\nameyeardelim}%
      \usebibmacro{cite:plabelyear+extrayear}%
      \savefield{fullhash}{\cbx@lasthash}}}%
   \setunit{\multicitedelim}}

\newbibmacro*{textcite}{%
  \iffieldequals{fullhash}{\cbx@lasthash}
% Compact cite - more than one thing for same author
    {\setunit{\compcitedelim}%
     \usebibmacro{cite:plabelyear+extrayear}}
% New cite
    {%
    \ifbool{cbx:parens}
      {\bibcloseparen\global\boolfalse{cbx:parens}}
      {}%
      \setunit{\compcitedelim}%
      \ifthenelse{\ifnameundef{labelname}\OR\iffieldequalstr{entrytype}{patent}}
  % No author/editor or patent
       {\iffieldundef{shorthand}%
    % Cite using title
         {\usebibmacro{cite:noname}%
          \setunit{\ifbool{cbx:np}%
                   {\nameyeardelim}%
                   {\global\booltrue{cbx:parens}\addspace\bibopenparen}}%
          \usebibmacro{cite:plabelyear+extrayear}}
    % Cite using shorthand
         {\usebibmacro{cite:shorthand}}}
  % Normal cite with author/editor
  % Normal full cite
       {\ifnameundef{shortauthor}%
    % Normal full cite
         {\printnames[labelname][-\value{listtotal}]{labelname}}
    % Cite using short author
         {\cbx@apa@ifnamesaved
           {\printnames{shortauthor}}
           {\printnames[labelname][-\value{listtotal}]{author}}}%
  % Year
        \setunit{\ifbool{cbx:np}
                  {\nameyeardelim}
                  {\global\booltrue{cbx:parens}\addspace\bibopenparen}}%
  % Put the shortauthor inside the year brackets if necessary
        \ifnameundef{shortauthor}
         {}
         {\cbx@apa@ifnamesaved
           {}
           {\printnames{shortauthor}\setunit{\nameyeardelim}}}%
  % Actual year printing
        \usebibmacro{cite:plabelyear+extrayear}%
  % Save name hash for checks later
        \savefield{fullhash}{\cbx@lasthash}}}}

\newbibmacro*{citeyear}{%
  \iffieldundef{labelyear}
    {\usebibmacro{cite:init}}
    {\iffieldequals{fullhash}{\cbx@lasthash}
       {\setunit{\compcitedelim}%
        \usebibmacro{cite:plabelyear+extrayear}}
       {\usebibmacro{cite:plabelyear+extrayear}%
        \savefield{fullhash}{\cbx@lasthash}}}%
  \setunit{\multicitedelim}}

\newbibmacro*{cite:post}{%
  \xifinlist{\thefield{fullhash}}{\cbx@apa@names}
    {}
    {\listxadd{\cbx@apa@names}{\thefield{fullhash}}}}
\makeatother

\begin{document}
\parencite{john_big_1991}
\parencite{john_big_1992}

\parencite{john_big_1991,john_big_1992}
\parencite{john_big_1991,john_paradigm_2008}

\parencite{john_big_1991}

\parencite{john_big_1991}

\parencite{john_paradigm_2008}
\parencite{john_big_1991,john_paradigm_2008}

\printbibliography
\end{document}

gives the (arguably) expected result of