I haven't found this strange problem anywhere so here it is.
When I move the mouse a little and simultaneously hit one of the shift (as well as Ctrl and Alt) keys the cursor jumps quite a bit towards the upper left corner at a 45° angle. This is especially annoying when trying to mark files with a mouse/keyboard combination.
So far, I have discovered the problem in almost every application EXCEPT MS Office, Opera, Thunderbird and utorrent.
Notebook: Samsung M60 Chartiz
OS: Vista Home Premium 32-Bit
Mouse: MS Wheel Mouse Optical + Synaptec Touchpad, same problem.
Drivers: default drivers and IntelliPoint V22.214.171.124, same problem.
Thanks a lot.