Snes9x.com

I've usually been able to handle doing SNES games using the keyboard, but upon trying to do super metroid, I hit the problem of not being allowed to use more than three keys at once for some reason. And since you basically have to tape the dash button down to do anything, this made things... difficult. So I tried to hook up the switch pro controller using a usb, which normally works just fine in everything else. But as I go to the input settings, as soon as I click the first box it starts rapidly setting seemingly entirely random buttons for every slot and refuses to go back up when I tell it to. I assumed it was the controller detecting something it shouldn't have, but I tested every button again just to make sure nothing was stuck. For some reason it just kept doing it no matter what I did. Is this a common occurrence? I don't really have any other gamepads on me right now.

Also, how do I fix it?