Vashj'ir has a quest called Bio-Fuel. You kill some creatures and then use a quest item on the corpses. The corpses despawn about 2 seconds later.
If you are a skinner, you are able to skin them if you click immediately after the quest item finishes. It waits just long enough for you to loot and then despawns.
This isn't gamebreaking, but I doubt it was intended. I don't like seeing skinnable corpses get wasted, especially with the AH prices right now.