Literature with Biber generates strange citations: firstnames appear erratically

Question

I had been using bibtex and then biblatex for quite some time. For the newest edition of my book I moved to biber. I happened t notice that firstnames are sometimes generated and sometimes not. Has this been observed by others?

I have tried to make a minimal example but without success. Using the following code, which shows all the commands related to biblatex I have in my preamble I could not get the firstnames to be shown. Even with the stylefile I made for this book (second line) the error did not occur.

I have a dropbox with the latex files for the book available. I can give access to these.

What do you propose?

\documentclass[fontsize=10pt,twoside]{scrbook}
\usepackage{hormonbuch}
\usepackage[%
  style=authoryear%
  ,natbib=true%
  ,sorting=nyt,backend=biber,doi=false,isbn=false,url=false]{biblatex}
\addbibresource{../Literatur/EndokrinologieKundeNourl.bib}

\renewcommand*{\bibpagespunct}{\addcolon}
\DeclareFieldFormat{pages}{#1}

\renewrobustcmd*{\enquote}{}

\renewbibmacro{in:}{%       Herbert Voss auf http://tex.stackexchange.com/questions/10682/suppress-in-biblatex
  \ifentrytype{article}{}{%
  \printtext{\bibstring{in}\intitlepunct}}}

\renewbibmacro*{journal+issuetitle}{%
  \usebibmacro{journal}%
  \setunit*{\addspace}%
  \iffieldundef{series}
    {}
    {\newunit
     \printfield{series}%
     \setunit{\addspace}}%
  \usebibmacro{volume+number+eid}%
%  \setunit{\addspace}%
  \newunit}

\renewbibmacro*{volume+number+eid}{%
  \printfield{volume}%
%  \setunit{\addcolon\space}%
  }%
%
\renewbibmacro*{note+pages}{%
  \printfield{pages}%
  \newunit}
%
\begin{document}

\citet{CRT+88,FDe+85}
\citep{CRT+88,FDe+85}
\cite{CRT+88,FDe+85} 
\printbibliography

\end{document}

Answer 1

This is almost certainly to do with using the uniquename and uniquelist options which are enabled by default in most bundled styles. These options mean that biber automatically disambiguates names by using initials or full names, depending on which other names are cited. See the biblatex manual which explains this with some comprehensive examples. If you set uniquename=false and uniquelist=false I'll warrant that the "strange" behaviour you see stops.

Answer 2

Most often this problem is caused by inconsistent author names in the bib file. For example, if the bib file contains some entries with

author = {Smith, John}

and other entries with

author = {Smith, J}

then biblatex will try to disambiguate these authors, by referring to either J Smith or John Smith.

One way to fix this is to turn off disambiguation, as suggested by @PLK. Another way is to make sure all your bib-entries have consistent names.