Looks like I accused start8 wrongfully...
First I repared the system files with sfc /scannow, but that didn't solve the problem. Then I created a new user account on my system and the problem did not appear so far. So I guess a corrupt user profile might be the problem (had this already a few months ago, back then it was caused by a falty windows update).
Sorry for blaming you, keep up the great work and thanks for your quick reply...
