Another workaround that I found was to do the following:
... Have vertical + horizontal centering switched on (as I do in 95% of my configs and it works well).
... Change the scaling from "No scaling" to "Default".
At least for Pang + Dino Wars this stops the scrolling / jumping issue; will test Alien Breed when I'm home tonight
I wonder what it is in terms of vertical centering that's different when using "No scaling" as opposed to "Default"?
Is it not possible to apply the same method when "No scaling" is selected?
Ignore these questions if they're silly, is not how things are supposed to work or will break something.
Sorry to be driving you insane Toni.