If you click on a slab with a water bucket it will get waterlogged, where it is partially filled with water. That is intentional, but if you do the same on a Jigsaw Block it will have the same effect.

Steps to reproduce:

1. Get a jigsaw block through /give
2. Get a water bucket
3. Crouch and click the jigsaw block with the water bucket

Expected result:

The water will be placed next to the jigsaw block.

Actual result:

The water is placed inside the jigsaw block.