When using multiple list-of on the same page they overlap

When list-ofs follow each other they overlap, at least with my setup. Here's an example:

test.tex

\documentclass[a4paper]{memoir}

\usepackage{xltxtra}
\usepackage{polyglossia}

% New list of source code listings
\newcommand{\sourcename}{Source Code Listing}
\newfloat[chapter]{source}{los}{\sourcename}
\newcommand{\listsourcename}{List of Source Code}
\newlistof{listofsources}{los}{\listsourcename}
\newlistentry{source}{los}{0}

\renewcommand*{\insertchapterspace}{%

\chapterstyle{pedersen}

\begin{document}

\frontmatter

\listoffigures

\listofsources

\mainmatter

\chapter{One}

\begin{figure} \caption{Some  fig} \end{figure}
\begin{figure} \caption{Other fig} \end{figure}

\begin{source} \caption{Some  src} \end{source}
\begin{source} \caption{Other src} \end{source}

\end{document}


Compile with:

xelatex test.tex && xelatex test.tex


This is the result:

I could add some vertical space, but is there a more correct way of handling this?

-

That's a side effect of the petersen chapter style. The definition of this style contains (among other things) the code line
\setlength{\beforechapskip}{-20pt}