Bonemeal in dispenser consumes the bonemeal even when there is no crop!

Happened on a server when bonemeal was in a dispenser surrounded by obsidian and I clicked a lever next to it.

WHAT I EXPECTED TO HAPPEN WHEN I CLICKED THE LEVER WAS:

Nothing would happen. The bonemeal would stay in the dispenser.

WHAT ACTUALLY HAPPENED WAS:

The bonemeal was consumed despite there were no crops.

STEPS TO REPRODUCE:
1. Place a dispenser, fill it with bonemeal.
2. Place a redstone torch, block, plate, button or lever next to it.
3. Make sure there are no crops nearby and click the lever.
4. Your bonemeal is gone.

(Note: Happened on a server that had NO plugins that modified bonemeal, and it works on singleplayer too.)