Not certain when/why this is occurring, but MAME 0.177 -- and rebuilt latest to 0.178 (mame0174-3247-g48774d6) -- shows a pixel or two rendered during gameplay.
Sometimes it's leftover near the last explosion(s), but sometimes you can see the rogue pixels appear anywhere in the city-silos-land areas. One time, the corruption occurred in the missile silo, for which the end of wave bonus counter got caught repeating itself as it accounting for "remaining" missiles and erasing them. That was extremely weird to see occur, not that I minded the screen-wrapping for a 100+ missile count!
I dropped all missile.* files from .mame and tried all three video modes: opengl, bgfx, and soft. All is repeatable.