I can't make my Sim play guitar!

I don't know if this is a glitch or something I'm doing wrong or what, but it's making me crazy. I have the Sims 3, Pets, Late Night, and Seasons. Everything's been going fine except that yesterday I changed one of my sims (who lives in an apartment) to a musician and bought him a guitar. I've gotten him to play it successfully once or twice, but most of the time (whether I click "Play Alone" or "Jam) he picks up the guitar, walks out of the apartment, and stands outside of the door (to an empty apartment that says "nobody lives here") and seems to try to get in. When he can't get in through the door he stamps his foot and returns the guitar to its stand. My sims are generally annoying about not doing things because they'd rather stand there tapping a foot letting you know that they're not at the right angle or whatever and starving slowly, but this is very weird and super annoying. Thoughts?