I ran into the same problem 3 times in the Citidel area. Also found that if you fight too close to a wall or a doorway there is a chance that loot will be stuck in areas you cannot reach. I have a tendancy to fight in doorways for crowd control (not really that effective in this game though, monsters seem to bounce around a bit) so did have to reload a couple of times. Just a minor annoyance.
My Hero did wind up in the black void outside the playable area one time and I could run off the screen into who knows where.
