Mixer only outputs Aux sends when headphones plugged in.

Took me a bit to figure out what was going on. I opened MuseScore today and plugged in my headphones. I noticed that the chart I was working on (only a Large Drum Kit) sounded like really wet reverb. I tried disabling the aux send, messing with levels, and finally unplugging my headphones was what "fixed" it. Plugging them back in, the problem remains. The levels on the Mixer indicate that audio is supposed to be outputting through the master, but it isn't. The audio device is set to System Default, but switching to Speakers (Realtek(R) Audio) doesn't help. Is this a known problem? I tried to search the forum but I don't frequent here often. I also am filing a bug report.