yea, i fixed it myself.
what i assumed in the edit of my post was really the case.
because i didn't do a clean install (with deinstalling the older version first) i was still on the old chain.
after deinstalling everything i did a clean install and synced the whole chain again and after that i closed it and replaced the wallet.dat with my saved one.
 
maybe there should be a hint or something that it has to be a clean installation and not just an update over the older version.