http://wiki.spiralknights.com/File:Stonewolvesglitch.jpg
In Clocktower areas the stone wolves will burrow out into 'space' (outside the playable area). Things to note:
1. Still killable with a handgun
2. Any drops that aren't magnetic will languish in space forever
+1
Floating drops: http://wiki.spiralknights.com/images/7/7a/Air.jpg
On a similar issue, if you kill an enemy near a gate, some drops can get to the other side of the gate, making them unreachable.