Hmm. I'm using the same ROMS that work flawlessly on my 3GS, but I get no picture of the games, only the sound and the joypad below. When I switch between 1x and 2x, I get a frame of gameplay, but nothing else. I'm having the same issues with both Snes4iphone and Genesis4iphone.
It looks like pixel doubling makes these games look like they're on an old school monitor. Maybe theres no need for any smoothing effects.
I have EXACTLY the same problem...
only 1 frame of gameplay when switching.