I've noticed that all the emulators I've tried either incorrectly render horizontally mirrored games. Start up an emu and play Super Mario Brothers 3. When you scroll right, various incorrect colors will appear on the different squares on the far right of the screen. What's more, is that there continually appears incorrect table data on the right side of the screen, the width of which depends on the horizontal scroll register. When the horizontal scroll is 4, then there exists a 4-pixel wide area of junk on the right side of the screen. When it's 5, it fixes itself.
NO (good) emulator I've seen does not produce these results. O_O Anyone know what's up?