Bugfix parity report for MC-4533 (mark as relates to), although the issue's manifestation differs slightly. I searched, but there didn't seem to be any tickets on the matter.

The bug

The shape of a fluid depends on blocks diagonally adjacent to it, which should not happen since there's technically no contact between these blocks and the fluid.

This was recently fixed for Java Edition (MC-4533), however an extremely similar issue to this still exists in Bedrock Edition, which this report concerns.

How to reproduce

1. Create an eight-block ring as seen in the screenshots attached
2. Place water inside this ring
3. Break one of the four corner blocks, and note how the water's shape changes with a corner moving down
4. Now look at the other screenshots, and place a water source "triagonally" adjacent (offset (1,1,1)) to the initial water, barricaded so they don't properly connect but such that it flows down into the diagonally adjacent block, and note how the water's shape changes with a corner moving up

Expected results

Neither of these actions would change the water's shape.

Actual results

They do.

Further notes

Where this issue differs from Java Edition pre-1.18.2 seems to be the fact that fluids can only form these erroneous geometrical connections to fluids on their same Y-level. The issue with connecting upwards (as seen in MC-70848) does not seem to manifest in such simple setups. A ticket on a similar equivalent case to this is upcoming.