running 0.11.0-pre-559 on fabric
this is a particular quirk with the allay.
when a player gives an item to an allay, the player is marked as its "owner".
allays are incapable of receiving any damage from their owner. apparently this is vanilla behavior.

with an allay mindflaying recipe, it's therefore possible to have an allay in a state where you cannot retrieve the item from it without killing it, but you cannot directly deal damage to it either. not invulnerable, but certainly a pain in the ass.

technically speaking, none of this is a bug, but it is strange behavior. perhaps the allay could forget its "owner" when brainswept?

Good reason to implement custom brainsweeping hooks a la the custom velocity hooks

OH, no it's that the InteractionResult variants mean different things on different platforms, I think...

This issue still exists on Forge. The item can sometimes be retrieved (inconsistent) but it won't update ownership since they're brainswept.