Structure template feature doesn't waterlog structure properly

When using add-on adding structure template feature - minecraft:structure_template_feature, if the feature is generated underwater and it contains waterloggable blocks, those blocks don't get waterlogged e.g. slabs, stairs.

Steps to reproduce:

• Create an add-on with any minecraft:structure_template_feature feature, the structure must contain waterloggable blocks.

• Add feature rule that allows it to generate in ocean biomes on Y level using molang query query.above_top_solid(variable.worldx, variable.worldz).

• Find the feature generated.

Expected result: 
Structure gets generated properly underwater with all waterloggable blocks actually waterlogged. Exactly like structure block loads structures.

Actual result:
Structure gets generated underwater, however all waterloggable blocks aren't waterlogged creating weird looking structure. Unlike structure block loads structures.

Note that the bottom slab isn't waterlogged as well, the visual glitch just isn't visible on it, however the top part of the structure shows the issue well.

Add-on with this issue is available to download here on mediafire, ocean_well files are the ones affected by this issue.