This looks like a bug.
Here is an ugly workaround:
\usepackage{expdlist}
\begin{document}
\ifx\HCode\UnDef
\begin{description}[\breaklabel\setleftmargin{1ex}]
\else
\begin{description}
\fi
\item[test1]text1
\item[test2]text2
\end{description}
\end{document}
Update: https://puszcza.gnu.org.ua/bugs/index.php?155
Update 2. The bug is closed. Until the patch travels to your system, just add the file expdlist.4ht
to your work directory with the following contents:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% expdlist.4ht 2011-11-20-04:55 %
% Copyright (C) 2007--2009 Eitan M. Gurari %
% 2009--2011 TeX Users Group %
% %
% This work may be distributed and/or modified under the %
% conditions of the LaTeX Project Public License, either %
% version 1.3c of this license or (at your option) any %
% later version. The latest version of this license is %
% in %
% http://www.latex-project.org/lppl.txt %
% and version 1.3c or later is part of all distributions %
% of LaTeX version 2005/12/01 or later. %
% %
% This work has the LPPL maintenance status "maintained".%
% %
% This Current Maintainer of this work %
% is the TeX4ht Project <tex4ht@tug.org>. %
% %
% If you modify this program your changing its signature %
% with a directive of the following form will be %
% appreciated. %
% \message{signature} %
% %
% tex4ht@tug.org %
% http://www.tug.org/tex4ht %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\immediate\write-1{version 2011-11-20-04:55}
%
% This work may be distributed and/or modified under the
% conditions of the LaTeX Project Public License, either
% version 1.3c of this license or (at your option) any
% later version. The latest version of this license is in
% http://www.latex-project.org/lppl.txt
% and version 1.3c or later is part of all distributions
% of LaTeX version 2005/12/01 or later.
%
% This work has the LPPL maintenance status "maintained".
%
% The Current Maintainer of this work
% is the TeX4ht Project <http://tug.org/tex4ht>.
%
% If you modify this program, changing the
% version identification would be appreciated.
%
%
% We just ignore optional arguments to description during ht run...
%
\let\description@orig=\description
\def\description{\@ifnextchar[% ]
{\description@ht}{\description@orig}}
\def\description@ht[#1]{\description@orig}
\Hinput{expdlist}
\endinput
`
, they'll be marked as code, as can be seen in my edit. You can also highlight the code and click the "code" button (with "{}" on it): this is better than<pre>
in most cases as it does syntax highlighting.