Good call, fiddler! I just did a reset to my setup and the stuck MIDI has completely disappeared.

Then I did an undo to see if it would come back, and it does. Hm. So I did a redo to make it go away, and it wouldn't. The BiaB started sounding really weird, and then crashed. So when I brought it back up, I restored to factory settings again, and it started out fine with no drone. But then suddenly it started droning again but stopped -- dunno why. So I went to change the DXi synth to something that sounds remotely like musical instruments and then it started sounding all weird again, and then crashed. I just brought it up again and it started out fine, but then started in on the droning again. F12 won't make it shut up, either.

So I thought this was a good call at first, but turns out it's still a problem. Plus there seems to be a problem with the way it's handling DXi's as well. I'll need to spend some more time with that problem in the hopes of better understanding it.