VBox 4.0.4 and Windows 7 SP1 - Graphics issues?

[smartysmart34]

Hi all,

I'm running a Windows 7 VM (32 bit, SP1) on VBox 4.0.4. GA are installed.
When I connect to that VM via Windows RDP (not the vrdp-server of VBox) from another Windows 7 SP1 system, I experience graphic corruption within some german educational games (Schlaumäuse).
When connecting to that very same Guest from a linux machine using an older rdp-standard, everything is fine.
I remember having read about some enhancements to the rdp-protocol being made by sp1 to optimize remote graphics.
Could this interfere with the guest additions? This would be the only possible cause I could think of due to the fact, that rdping from linux works.

Kind regards,
Martin