While playing the recent snapshot I've had two bows, a diamond pick and a diamond sword all disappear. All had at least half health, and there was no breaking sound or animation.

The only correlation I've discovered is that I was fighting skeletons at the time. Most recently I was working on turning a skeleton dungeon into a trap, I was shooting them with a healthy bow but as one shot me as I was drawing the bow, the bow vanished from my inventory.