I just finally started playing Ultima Underworld 2 and I started encountering a problem involving the Avatar moving backwards despite not pressing any of the movement keys or using the mouse at all. I've been trying to figure out why the game is making the character move backwards and I have been trying to debug it. I unplugged my usb keyboard and mouse and it still moved backwards. I tried loading up separate save files and it moves him backwards still.

I jammed at the movement keys and its not like its some hung up key. I can move forwards or around but its still acting like the backward movement is still held down. I went so far as to make a new save file, a fresh start and its done it again.
I have not gone so far as to uninstall and reinstall a fresh install but I just might do so as I'm not even that far into the game.

Have any of you guys seen this kind of bug? I have been trying to google it and there seems to be no mention of it at all.
I have been playing windowed and alt tabbing but it didn't seem to effect the gameplay at all.

What a weird bug! I assume you've restarted the computer to make sure there is no Windows shenanigans going on? I've had Windows mess up like that on occasion. This game is also a bit different in that 'x' is the backwards movement key too.

With my playthrough of UUW 2 I had updated my DOSBox to a newer version and installed the mouselook patch and everything ran smoothly. Mind you, I don't recall if I played through with the mouselook patch as I had setup my game to give me a choice of which control style to use when I started.

Anyways, if you wanted to try a different DOSBox version I would try either ECE or Staging. Both are actively worked on and are good choices. You do need to be comfortable/willing to edit the dosboxULTIMA2.conf file though, as the newer versions will use slightly different config settings (ECE will likely need the least changing, while Staging uses the more modern SDL2)

If you want to try the mouselook patch, you'll need to extract game.gog (Try the newest 7-zip) to a separate folder (I named mine CDROM) and run the patcher on the files there. You can then edit dosboxULTIMA2_single.conf from: to (assuming CDROM folder is in GOG\Ultima Underworld 2) Mouselook: https://github.com/JohnGlassmyer/UltimaHacks
DOSBox Staging:https://dosbox-staging.github.io/
DOSBox ECE: https://dosboxece.yesterplay.net/

OH LORD, I didn't think to check my peripheries. I have a PS3 knock off controller that is USB and I just checked to see if it was interfering with it. I unplugged it and booted up UU2 and I could not move. So I shut off the game, plugged it back in and booted it up and my left analog stick is controlling movement. I think this is the reason why its giving me guff. I guess I'll have to look into the DosBox Config and disable joystick support, lol. I appreciate the post, I was worried It might be deeper than that.

I'll investigate this and post back and then see if It fixes it.
Well what do you know, problem solved! The whole backwards movement thing is gone and now the Avatar is stationary and not doing the moonwalk. All i had to do was go into the dosboxULTIMA2.conf and find the joysticktype value and set it to none. I guess the problem is solved for now. I guess let that be a lesson to everyone to check their peripheries and make sure DosBox doesn't decide to see it and make you moonwalk.