I just had my fully trained, maxxed out, fully equipped, lots-of-healing-potions goon squad destroyed when I sent an unremarkable slavegirl to the dungeon. She had -20 rebellion, and she'd been refusing to sleep with customers since pretty much forever. I'm starting to think "Big Boobs" is the new "merciless".
Another odd one: I've taken to taking all my goons off guard duty before i send anyone to the dungeon, just so I don't get them wiped out. Sometime they go quietly, sometimes they run off and get recaptured next turn, and in one case just now, sometimes they put up a fight and beat themselves up on the way to the dungeon.
Even with -100% rebellion and 100% happiness, slave girls still sometimes refuse to work. Pretty regularly. Every turn, in fact. Lesbian, Big Boobs, Lolita, Nerd, Cute, Strong Magic.
Tcha! It's like a disease. about five of them now, all at -100%, all refusing to work.