The bug

When you empty a water bucket while looking at the solid face of a partial block like a staircase or a slab, the water becomes waterlogged in the partial block instead of being placed above it.
There are 2 screenshots below of a 3×3 platform of slabs, one before emptying the bucket and one after emptying it. You would expect the water to be placed on top of the slab if emptied on the top face and waterlogged if emptied on the bottom face. Instead, though, the water is waterlogged, which is not the intended behavior (I think).