Fast user switching via Screen sharing

I came across a strange behavior. When I connect to a remote machine via screen sharing and try to change into a different account +(which is already logged in)+ with fast-user-switching the screen turns black for a moment and the new user desktop shows up. If I try the same by starting a new user session with fast-user-switching I can see the password request for that specific account but when I hit ENTER the screen stays black, nothing happens at all. Reconnecting via screen sharing doesn't help nor attaching a flat screen to the remote machine. All I can do is reboot via ssh. Is there a solution? Tried google but it didn't came up with any useful results.