Spreading speed of water should be guaranteed to be faster than that of lava in the Overworld. However in the current implementation, water is only statistically faster and has a small chance of getting overtaken by lava.

This is usually not a problem and could even be WAI but for smooth stone generators the difference of speed is crucial.

Steps to reproduce:

1. Open the attached test world.
2. Push the "reset" button to initialize the state of the contraption.
3. Grab some coffee while looking at the machine absent-mindedly. It may take several tens of minutes to pose the problem.

What I expect to happen:
The machine keeps generating stone blocks indefinitely.

What actually happens:
Flowing lava occasionally lands on the air block in front of the piston, before the water stream pours into the said space. When this happens water ends up flowing into the lava stream horizontally, which does not generate any blocks as expected, and finally the lava stream tries to flow horizontally into water, generating a cobblestone block blocking the water stream and the machine is dead.