The player cannot place a water source block on top of an upper slab.

Description:

Using a water bucket while aiming at an upper slab places the water at a high of a bottom slab. Water appears a block lower than it should.

Steps to recreate:

1. For ease of reproduction, place a full block on the ground.
2. Place an upper slab on the side of the block.
3. Aim at the top side of the slab.
4. Use a water bucket.
5. Observe the result.

Observed result:

Water source block appears beneath the slab despite using the water bucket on top of the slab.

Expected result:

Water source block appears on top of the slab after using the water bucket on top of the slab.

Attachment: A video comparing where water and lava appears after using buckets filled with corresponding liquids on top of an upper slab.