Imps behaving strangely, with Doom2 map05 in the yellow keycard area when the four imps saw the player and "woke up", they took a step and fell straight down into the water pool.
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It's almost like their "travel-over-cliffs"-bit would have been temporarily switched on. And for some reason this occures every time I have tried, but haven't seen anything such happening elsewhere.
BTW, the monsters can also activate fast lifts (WR/W1 types 120/121), and open some (but not all?) fast doors (DR/D1 types 117/118). (Doom2: map05, map02,...) Should this happen?