I've noticed an odd change in the way wuauclt behaves on startup after installing previously detected updates. It still does a detection but it's now inaccurate.
There's a workaround but if you aren't careful, you might be fooled into thinking your system needs updates it doesn't actually need (and vice versa).
My typical procedure for checking update status in my test environment has been to monitor C:\windows\windowsupdate.log (via dir) after a reboot, and when the file stops changing, look at the tail of the file to se if it says "0 updates detected", then do a <tt>wuauclt /reportnow</tt>, refresh the group view in the WSUS console and see if any new updates are needed.
But now, unnecessary updates are appearing as needed and necessary updates are not appearing. windowsupdate.log's detection status says "0 updates detected" and the time stamp is post-reboot, but WSUS reports that some superseded updates are still needed. The updates that had just been installed appeared as installed. The superseding updates have no status.
The workaround appears to be doing a manual <tt>wuauclt /detectnow</tt> after the client has settled down post-restart.
After this extra /detectnow then /reportnow cycle, the superseded updates appear as not needed for the system in the WSUS console, and the superseding updates appear as needed.
The latest episode was with 2953522 superseding 2964358 on Server 2008. (It was disconcerting to see that the update with the lower KB number was thenewer update, BTW).