Water looks like it flows up

The Bug

I was using a sponge to empty out a ocean monument, and the water, when finding a corner or an edge, would flow up to cover the empty block instead of flowing out.

How to Reproduce

1. In the ocean monument, use a sponge to clean out most of the water
2. Make sure there is only one layer of flowing water at the edge

Observed Behavior

Water appears to flow upwards when nearby water is at a higher elevation.

Expected Behavior

Water would not appear to flow upwards when nearby water is at a higher elevation.