The Bug: Regular caves in 1.13 snapshots will generate without causing block updates to nearby blocks like gravel and sand (Which is the way it has always worked), But water filled caves cause block updates when generating, which creates extremely strange looking cave generation, and it is also inconsistent (compared to normal caves, normal ravines, and water ravines)
What I expected to happen: Water filled caves would generate without the sand blocks updated (like the second screenshot but with water)
What really happened: Water in the caves has updated the surrounding sand (like in the first and third screenshot)
Steps to reproduce: Use the seed 16 and teleport to -200 80 900 to find a good example of a glitched cave.

(Also in the first screenshot, it shows that the sand hasn't been updated at the same cave above Y:63, which I think better shows the cause of the bug)