[NTVDM] Commander Keen 1-3 horizontal scrolling is jumping back and forth

This is nothing recently introduced, has been like this since I tested it the first time in Feb2015.

current Head r69731 is affected.

When you horizontally scroll in CK1-3 map screen and in-level,
the scrolling is not smooth, but jumps back-and-forth.

As if you would render an interlaced video after improper deinterlacing with wrong field order.
E.g: instead frame sequence 1,2,3,4,... you'd see 1,3,2,4,...

Vertical scrolling is working fine though.
see react-2015-10-28T19-47-36-968750000Z.webm

CC theflash