In Sonic 1, Sonic 2, and Sonic 3 and Knuckles, there's a funny little bug regarding how you move; if you hold both the left and right buttons together, your character will slowly walk to the right; if you push up against an object, the player will start flipping back and forth rapidly or (rarely) display the normal pushing animation backwards. An odd little bug, indeed. I'm kinda shocked by its' existence in all the main Sonic genesis games...
Are you serious? You call that bug? Tell me how do you press left and right at the same time with the MegaDrive control pad :/
Why? That's like being shocked that the first Crash Bandicoot game doesn't have analog stick support.
I could have sworn one of the MD dev manuals demands that games properly handle this. According to it, an MD controller can be worn down to the point of L + R/ U + D being doable. Right, the page is Correction-01.gif, in sega/Bulletins/Misc of the 32x DDK.
Oh man, what a riot! A standard Mega Drive/Genesis controller is designed such that the D-pad tilts on a central axis. This ensures that (similar to a joystick) both; left and right, or up and down, may not be pressed at the same time. One such chance of a standard controller being able to perform such impossible task, is if the rubber becomes worn from excessive playing. As Clownacy stated, this was mentioned in a bulletin, marked on "April 2nd 1991", two months before the release of the actual game, whereby the game would have likely have been in the hardware manufacturing process or nearby, and thus too late. I don't claim to know if the bulletin is right about the controller becoming worn, but the idea that the problem can be solved by rereading the data from the controller port is highly questionable. What were they expecting to do if it's a reoccurring state? Keep the game trapped and locked in a never ending read loop, until the player lets go of the controller? Let's be honest here, right or wrong. The game works fine and only emulators seem to avert into the problem, I've never had a problem on hardware. I would therefore place this into the category of, not necessarily "incorrect emulation", but "a mishap not worth bulging at".
Hm... I didn't realize the hardware prevented this (I don't have an actual Genesis myself). I did check my Nomad after reading this, though, turns out it does prevent this issue from ever actually occurring on a proper, unmodified and uninjured console. My bad XP. Still, it's a little important to mention though; most people will just play hacks in an emulator, regardless, so a fix for emulations sake could actually make sense.
There are many games which do bizarre things if you press left+right at the same time, since that's hard (but not impossible) to perform on the real hardware. Wonder Boy in Monster Land and Zelda 2 come to mind...
Isn't it emulator specific? iirc I got different results say in Gens and Regen. In one I think Sonic would just turn left and right every other frame while moving in whichever direction i pressed first, and in the other he'd just freak out. It's been a while so I might just be tripping balls.