I made an account here purely to say I have this problem too and it's driving me insane!
I (very generously and not only for her blood) moved in a townie that didn't have a place to live on the map. She has the good, outgoing, and cheerful traits so no harm, eh? I should have known she'd be trouble when the very first action she did on her own free will was donate $100. =.=
I didn't want to play her as a Sim, so I have free-will set to max and I let her do her own thing almost 24/7 and she will use the computer to donate $100 at LEAST every other day. I've only recently started taking a note every time she does it, and she's done it just 12 times since I've started taking note just yesterday.
She now lives locked in a 12x10 room with a tiny bathroom and a cooler to survive on because I've had it. =.= Please don't let this bug get forgotten!
Edit: I have no mods installed.