Windows 7: program installed with inexistant group or username in security tab

Hello all.

I have a very strange problem and I have looked hard on the net to find an answer with no success.

When I install any application, shortcuts are correctly installed in the windows menu as it should be. But when I reboot the computer, the shortcuts completely disappear. I have found the way to recover them: I open the shortcut properties, and under the shortcut security tab, my username is not in the list of group/username, but there is an unknown username in the list, something like s-1-5-5-0-663007, for example. If I remove this name and put my username, everything is fine. But this bothers me, this is not normal and may hide an important problem, and it is rather annoying to do that everytime I install something.

I have used 3 different antivirus to make sure I have no contamination. I must say I had a few severe ones in the past 3 months, all apparently well cleaned.

Any help would be great!!!

Thank you

Gaétan