I am running XP SP3 v.3244 (kb936929) x86.
After uninstalling an anti-virus program, the WMI entry for the anti-virus program in Windows Security Center is always removed.
But after reboot, sometimes the deleted WMI entry reappear and thus WSC reports that the removed anti-virus program is installed.
This problem does not occur on XP SP2.
It seems the deleted WMI entry is restored after reboot.