Painted non-full blocks don't stay waterlogged

[WenXin20]

Minecraft v1.14.4
Forge v28.1.90
MC Paint v1.4.5

• If a the back of a stair block is painted while it is waterlogged, it loses the ability to be waterlogged.
• The hit box is also finicky, attempting to step on the stairs will push/bounce the player off of it.

[ThePoshTux]

This also appears for other non full blocks like slabs (lower or upper) and Quark's vertical slabs. Looking at how faces of neighbouring blocks are being incorrectly culled and the hitbox is incorrect, leads me to believe that when painted, the model of a solid block is loaded. A button can even be placed upon this invisible full block.
I'm presuming your Process is to save the faces and associated faces of the block, replace the block with the associated canvas block (who's model is a solid block causing this issue) and then applying the faces of the original block.

Minecraft v1.16.5
Forge v36.0.46
MC Paint v1.6.2