Mah tools!

To reproduce:

1. create valid carpenter's table recipe with wooden hammer
2. place wooden hammer with max durability in the tool slot
3. place a different wooden hammer with max durability in the hotbar
4. shift + click wooden hammer in the hotbar to swap the tools
5. pick up the wooden hammer in the hotbar
6. savor the sweet loss of your tool in the tool slot

Seems to only happen with tools of the same type with max durability.