Hi
Just to let you know and if every anyone else stumbles upon a similar problem. I found it and solved it but I am not sure why it really happend.
My case:
An all my computers I have set the language to English and the locale to German(Swiss). This was working fine for Win XP, Win 7 and Win 8. Unfortunately Win 8.1 had some little problem with it. Even though it showed me the correct settings it messed around with them under advanced of the regional settings. The times, the currency, etc were all correct just the number tab had some mixed up stuff in it. I never changed that but I am not sure if I just got a buggy installation or if windows 8.1 pro has a problem with this kind of setting. Either way, setting the correct values manually solved everything.
So case closed for me as well ;)