While writing my thesis I found a problem of the nomencl package in conjunction with the KOMA-Script classes: the header is not changed from the one which is used in the section before the nomenclature section. A simple change of \thenomenclature works. Just add the following into the preamble:

\makeatletter
\def\thenomenclature{%
{
\@ifundefined{chapter}%
{
\section*{\nomname}
}%
{
\chapter*{\nomname}
}%
}%
{
{
}%
{
\makeatother