Ok after several reinstalls and tests, things changed a bit but not yet good.
I can connect via wifi, though the mentioned bug forces me to turn wifi off and on after every reboot. With wifi working i can access via ssh and samba, so i got my games on the pi by now, but i can't get a connection to the webinterface.
Also to me the systems seems very slow, sometimes i wait for a minute after clicking on network for example.
Hope you may have some suggetions for these effects.
Thank you.