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:
Get a jigsaw block through /give
Get a water bucket
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.
Structure blocks have already been reported at MCPE-59566, so I have removed them from this report.