Relates to MC-93468 as both are responsible for anisotropic water behaviour.

The bug

When a water source is removed from a flat surface after being allowed to spread fully, it decays at the same rate in each direction. However, if that water source isn't allowed to spread fully first, the decay ends up reverting to a lower symmetry.

The same can be seen with lava, which may make the reproduction steps below easier due to its decreased flow rate.

How to reproduce

1. Go to a flat area (about 10 blocks in each direction should have no raised or lowered regions)
2. Place down a water source
3. Wait until the flowing water reaches two blocks away from where it's placed
4. Quickly remove the water source before it reaches the third block

Expected results

The water would decay equally in all four directions.

Actual results

The water decays much faster along the X-axis. For the Z-axis, both sides disappear at the same time, but the north ends up with more water.