[NTVDM] major graphic distortion when playing Commander Keen 6

TRUNK r68094

This issue is reproducable when playing CK6 in ROS.
At the beginning of Level2 (Guard post1) suddenly graphics gets messed up totally.
It always starts exactly there (tried 3times) while level1 runs totally fine.
SVGA-compatibility-option within CK6 does not make any difference.

Attached is ROS-log, video demonstrating the issue and the game itself.

This seems somehow related to
https://jira.reactos.org/browse/CORE-9794
however, I retested r68084 and its broken too...