digitalRogue, I wonder if you would mind checking something for me seeing as you also have an audigy card. Read all the following b4 hitting the link though....
Hmm, the first plays fine and the second wants to default to WMP, so no idea (I can play with it more later, getting ready to settle in with a movie right now). However, I DID have a similar problem the other day before I rebuilt my system. I was playing MIDI files from a website through MC and I later noticed I had two instances of mediacenter.exe running. After killing the rogue process, I noticed at some time later that the MIDI files were playing softly in the background, in a continuous loop. I could adjust the volume of the MIDI in control panel, so it was a responsive process, but nothing I did would stop it, including running another MIDI file, for it would simply layer on top of the rogue music. A reboot solved the problem, obviously, but I thought it was an isolated incident. Perhaps not?
I am not sure which version of MC I was running at the time, but it was either 9.0.180 or 9.1.217. Earlier today I installed 9.1.218 on my fresh OS build, so that is my current version.