Summary: Pandas will "eat" an item, but then drop it when the animation finishes. They can also pick the item back up, but don't continue eating it, fortunately not creating a loop. This happens around 50% of the time.

How to reproduce:
1. Summon a panda and drop a cake (You cannot directly feed pandas cake in my experience, due to MC-234064)

2. The panda will start the animation of eating a cake when it picks up the item.

3. Wait near the panda and 50% of the time, you will hear an item drop noise when the animation finishes. If you are close enough you are able to pick up the cake before the panda picks it up again.

Notes: Lazy pandas for some reason only drop cakes 20% of the time. Worried pandas do not eat cake at all; as a matter of fact, they do not eat dropped bamboo or cake, but for some reason, they do eat bamboo if directly fed by the player; they pick up the cake, wait a random amount of time, then drop it 100% of the time, which after that they can pick it up again.