Nah. When you use the hide marker and go back to live mode, the room where the marker was goes black so your game doesn't have to work it's ass off showing what is going on everywhere. Think of University in S2 but blacked out. As long as there are real walls around, it will black out, but foundation walls confuse it. Maybe it thinks it's outside or something.
Like I said, I fixed it so there's less showing but I don't know if it would be an eyesore to people who send their sims downstairs to the gym, or do laundry in the little room I left space for. I guess I can just put a warning up. Actually, I should send you the basement apartment one itself to make sure it will even install.