The water flow patterns are sometimes inconsistent and unpredictable.

What I expected to happen was...:
I expect the water to flow in a pattern the shown in screenshot minecraft-waterflow1.png

What actually happened was...:
The water sometimes fails to flow in some directions, as shown in screenshot minecraft-waterflow2.png.

Steps to Reproduce:
Unfortunately, the unpredictability of the issue makes it difficult to reproduce from scratch. I can reproduce it in my current world simply by placing water on that cobblestone block.