# Literature with Biber generates strange citations: firstnames appear erratically

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}

\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}%
\iffieldundef{series}
{}
{\newunit
\printfield{series}%
\usebibmacro{volume+number+eid}%
\newunit}

\renewbibmacro*{volume+number+eid}{%
\printfield{volume}%
}%
%
\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}
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