This strikes me as the sort of thing you'd have noticed and fixed, but in 1.09B it seems as though if you either move around a lot or ram the spacebar fast enough, and there aren't any monsters next to you, you can force all of the monsters to remain completely stationary. Needless to say, this makes using DOTs and mine spells extremely easy and kind of breaks the game.
Some of this has been fixed for 1.0.10, some of it still happens. The more obscene instances have been fixed.