The bug
Shift-clicking water buckets against a waterloggable block doesn't place the water against the waterloggable block.
Example
[media]→ ❌ Shift-clicking the water bucket against the slab should place the water on the redstone block, like it would when shift-clicking a bucket against a cauldron.
Might be hard to fix or just wai. Notice that you need to shift click to waterlog chest without opening it.