Comment # 53 on bug 1182666 from Stefan Dirsch

Hmm. I believe the behaviour is correct. You need to look for %triggerpostun
script, not the %postun script.

# rpm --triggers -q  nvidia-gfxG05-kmp-default
triggerpostun scriptlet (using /bin/sh) -- kernel-default
for dir in $(find /lib/modules  -mindepth 1 -maxdepth 1 -type d); do
        if [ ! -d $dir/kernel ]; then
                test -d $dir/updates && rm -f  $dir/updates/nvidia*.ko
        fi
done

modules in updates/ are only removed if there is no kernel/ subdir any longer,
i.e. no modules are longer installed.