Water source won't spread over sea pickles

Usually when two streams of level 7 flowing water collide, a new water source will form. This doesn't happen when the block space which is supposed to become a water source is right above sea pickles or kelp. This relates to MCPE-34237 but isn't exactly the same, as this doesn't affect any other waterlogged partial blocks.

Steps to reproduce:

1. Dig a 1 high, 3 wide, and 2 deep hole.

2. Place 3 water sources on the first layer.

3. Place sea pickles on the center block.

4. Place 2 water sources on the left and right sides of the second layer.

What I expect:
A water source block forms on the center of the second layer, right above the sea pickles.

What actually happens:
The center block becomes a level 8 flowing water instead of a water source.