The thing is that most of these people don't have copiers or flash cartridges to test on hardware. So they use the most popular emulator to test as they go along. Naturally that emulator lets you do a million and one things real hardware won't allow, and they don't even notice.

The biggest one is that VRAM writes are not allowed during active display. To fix this, you add this code inside vram_write():
if(vcounter() < (overscan() ? 240 : 225) && !display_disabled()) return;

Won't break any known games, will actually *fix* Hook (U) garbage in the intro, an active bug since the very first release.

I was told some games were too timing sensitive, which I don't believe, but okay fine. Adjust the range. instead of 240/225, do 245/230. It's not perfect, but it'll give a lot of extra coverage for bad timing.

But nope, still not fixed. Just off the top of my head, it's broken the following fan translations:

Dragon Quest 1&2 Reprise - title screen graphic broken <broken forever, patch author is dead>
Dual Orb 2 - Yes/No menu broken [updated patch fixes it]
Mystic Ark - text is invisible [updated patch fixes it]
Sailor Moon - Another Story - intro text is corrupted <broken forever, patch author vanished>
Ys IV - no text is visible in dialog boxes [updated patch fixes it]

I've also hit this bug myself when I first found out about it in 2000 or so. I'm sure there are many more examples.

I've gotten at least three false bug reports on Sailor Moon, one on Mystic Ark, and two or three on ROM hacks. People see it working in ZSNES and assume the bug is on my side.