5.1.1.371 consistently crashes when attempting to view the attached demo for TCB: The Undercity: 3N2E with the following in drod.err.
Assertion error in line 2197 of Monster.cpp: "this->CanDaggerStep(pMonster->wType, false)"
Assertion error in line 2198 of Monster.cpp: "bIsStalwart(this->wType) || this->wType == M_GUARD || this->wType == M_SLAYER || this->wType == M_SLAYER2"
Assertion error in line 3406 of DbRooms.cpp: "this->pMonsterSquares[ARRAYINDEX(pMonster->wX,pMonster->wY)]==pMonster"
The demo plays back normally in 5.1.0.6512. I can't see anything obvious in the changelog that would affect this room, but if some logic change has invalidated this demo, I would expect the game to gracefully reject it, however, it imports with no problem and only crashes on playback.