-There was a single acacia leaf in a chest.

-It was in the first slot of a double chest.

-The chest was used for storing Dark oak, so it was peculiar to see the acacia leaf in there.

-I tried moving it, but picking it up would immediately place it back in the slot.

-It could not be moved or removed.

-I broke the chest to see if there was any result.

-I picked up the contents from the broken chest, including the acacia leaf.

-The acacia leaf had the same behavior in my inventory, it cna not be moved, placed, picked up, or interacted with in any way, and it is now STUCK in my inventory!