Cant click group similar task bar items in start menu randomly ?

I have this problem under Vista x64 sp1 with all the latest updates..
it happens radomly and only a reboot fixes the issue..

I have it set to the default of group by similar task bar items, so if
i have 10 explorers open and i want to click one of them, it just
minimizes..

The same holds true in the documents folder, which i have set to auto
expand.. it will expand but i cant click any subfolders (from the
start menu)..

I dont know if any apps i have down there could be causing it and even
if they did, i'd need a fix to still be able to have them running..
ie: Utorrent or Outlook, Servu etc..

Or if it is a different issue..

Anyone found a fix for this?

Thanks