Ignore me I have just worked out to disable cache. Unfortunately it doesnt solve the problem.
Regards
Steven
As myself and others have asked, are these tests being done without the Pi. As if your having same issue, then it is not likely to be anything related to PiSTORM.
An example of a 500 floppy game that glitches on an A1200, is Dune (the original adventure).
You need do some tests with no Pistorm connected and then with it connected. Mschulz is correct though, best way to run games, is via WHDLoad (+WHDLoad wrapper).
If your able to get stuff running fine via vanilla setup, you could try what was mentioned. Adding a disable function, so your able to disable PiSTORM without removing it.
I know its a lot of information to take in and can get confusing.