Just in case someone stumbles over this:
I just installed a fresh ubuntu 12.04.2 64bit server and I installed samba in the ubuntu installer.
Unfortunately this seems to install a buggy version. After spending two hours of search I just tried to remove samba and it told me, that it is not installed... so I just installed it and now the bugfixed version seems to be installed and is working.
Just in case someone stumbles over this:
I just installed a fresh ubuntu 12.04.2 64bit server and I installed samba in the ubuntu installer.
Unfortunately this seems to install a buggy version. After spending two hours of search I just tried to remove samba and it told me, that it is not installed... so I just installed it and now the bugfixed version seems to be installed and is working.