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 || :
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