Sword dissapears when fighting mobs (even without armor)

I'm reporting an issue where in the middle of a fight with mobs your sword will dissapear from your hand.

The world this happend in was created in 1.8-pre2. When it happened the client was version 1.8-pre3.

I encountered two accurances of the dissapearing sword. First time I was fighting a hoard of zombies+creepers so I don't know which one I hit or if maybe I hit a zombie with some armor.
The second time I was standing by a fence and fighting two baby zombies over it when my sword dissapeared. I don't think they were wearing armor.

If you need any further info just ask,
cheers