Multi Monitor issues on 2008 R2 RDS

I have a problem concerning the multi monitor support of a terminal server 2008 R2.
The users are connecting from a thin client with a linux OS.
The remote session uses both screens but identfies them as one big screen, so you cannot use them seperately. Maximizing a window will span across both screens which makes working impossible.

I tried to reproduce the behaviour on a test server but it works fine there. I used the same environment: 2008 R2 TerminalServer and Fujitsu Futro S700 thinclient.

bad server:

Working server:

What may cause this?