I'm working on JJXB's Double Dragon II 3DN and I now see what he meant by "garbage at the bottom of the screen buffer". See photo below for explanation:
I checked this out on a regular emulator, and sure enough it shows up there too, so this is a problem with the original game.
Would it be possible to mask this in your emulator without removing the sprites when they are supposed to be used?
I figure it's probably not possible, but thought I should ask.
As you can see from the picture below, this can be hugely distracting from the information at the bottom of the screen when it gets out of hand. I never really paid it much notice on the original game when the sprites aren't being expanded, but now that they're 3D you can't read anything when this happens.
Wow! Look how the numbers from the bottom of the screen show up at the top while going up the ladder!
I wasn't able to verify this happens without the emulator, but there definitely is a constant mess of garbage without the emulator on the top and sides as you're moving around. We'll probably just have to live with it, but it's a shame that these minor annoyances are so prominent once you 3D the game.