My IBM EGA card, fully upgraded to 256KB, has an issue with Commander Keen's later graphics engine. The issue is randomly wrong-colored pixels appearing in the main game. These pixels can be "corrected" in many places by scrolling the so that they are no longer visible on the screen and then returning. However, often new randomly colored, wrong pixels will appear. Sometimes there are a lot of pixels, sometimes only a few.

This issue does not occur in other EGA games I have tried with this card, including games like Secret Agent and Commander Keen 1-3 which also use EGA panning registers for smooth scrolling. I have an Everex EV-657 EGA card which works flawlessly with Keen 4-6. I have tried the IBM card on a PC/XT and a 486DX2/66 and both systems exhibit the same behavior. I have also tested the IBM card with the official diagnostics diskette and a third party application, CheckIt. Both programs report no memory errors or other errors. I have also tried all the options I am aware of that may affect the video rendering : /nopan, Fix Jerky Scrolling and SVGA Compatibility fix. I have also tried the patch here : Keen 4-5-6 choppy scrolling on EGA card. Nothing has been successful.

I have taken some screenshots with my Datapath E1s to demonstrate the issue. The first image shows the level in Keen 4 on the IBM EGA card as you enter the level :

The second image shows the same area after you enter and exit the stone building :

I may do a cross-post on the VCF forum

Finally, the third image shows what the Everex EGA card will display :

So, is this an issue anyone has found with their EGA cards and these games, or does my card have some subtle flaw or damage which this code shows?