Observed Behaviour:

Right-clicking with an Empty Bucket, Water Bucket, Lava Bucket, or bucketed Aquatic Mob on an interactable block (such as a door, note block, or decorated pot) or item frame, that is behind a targetable (but not right-clickable) entity causes the bucket to be placed, as if the player was sneaking, which is otherwise required to place against these surfaces.

This applies to all targetable entities (those who display target information in the F3 menu) except armour stands, unless they have their own specific right-click interaction (when holding that item).

This behaviour seems related to the fact that entities, including mobs, do not block placement of water or lava even when their hitbox is obstructing the target surface. Assuming that this is intentional behaviour, an exception should exist when the target surface ordinarily requires the player to sneak to place against it.

Expected Behaviour:

Either:

1. The player interacts with the surface regularly (e.g. opening a door, storing the item in the decorated pot or item frame, changing the pitch of the noteblock, or toggling a daylight detector) as if there was no mob in the way
2. Nothing occurs, as with right-clicking any other item on the target surface with a mob in the way.

Steps to Reproduce:

Open up a creative world, and use the /tick freeze {}command. Place down a decorated pot or other interactable block, then use a spawn egg to place a pig in front of it. Right click on the block through the pig, and the item is placed.

To test empty buckets, you must use a waterloggable block such as a decorated pot or trapdoor, as bucketing water in front of a block is expected behaviour.

Included images show before and after of these tests.