I noticed that on maps with lava creatures and Imps tend to cut corners while walking near it. In case of Imps they will drop traps/specials/bodies and they will float there for ever (especially annoying when there is no bridge available) Creatures will just die if it happens too often before they reach food or lair.
It mostly happens when there's a curvy path along Lava. But on the 2nd undead campaign map (*something* Cathedral) it also happens on the "bridge" to the cathedral which is straight..
I'm not sure if it's related but Imps and creatures also seem to know the map before it's visible. They always take the shortest route even if that means breaking through enemy doors. A claimed path should be used if available in my opinion. Unless of course it's a scouting creature like a hound or fly.
Using ver 0.5.0.3081