Given that you can just exit and restart, it's not the end of the world. Still, seeing how long this game has been in development, I don't really understand why not more work has been put into eliminating such setups. This is not rocket science. Rather, graph theory.
I have had another thing today in the southern swamp, where in the lower left corner of the level there was an area which was completely unreachable for me, and there was a monster inside (and God knows what else ). I was a fighter apparently so I could see the location of the monster.