The water is flowing the wrong way.
How to reproduce:
Create a creative world with the seed 76990025
Teleport to 55 13 -219
Start facing to east
Mine straight until you get to (67 13 -219)
Expected: Water flows both into your mining place and to the rest of the cave.
Result: Water flows only to the cave.
Environment
Windows 10, Latest Java 01/11/19, Optifine (which should'nt change the water physics in any case.
Decent Computer
Seems fine to me. Water always tries to find the shortest way down.