Please see
http://lists.fedoraproject.org/pipermail/devel/2011-April/150540.html
Julian's followup post gave an example of how to fix the scriptlet:
%postun
if [ $1 -eq 0 ] ; then
glib-compile-schemas %{_datadir}/glib-2.0/schemas &> /dev/null || :
fi
%posttrans
glib-compile-schemas %{_datadir}/glib-2.0/schemas &> /dev/null || :