While I was playing in my new survival world, I came across a lava flow and I wait for it to reach the water. When it got to the bottom however, It just abruptly stopped flowing. The lava was generated and not hand-placed. I expected the lava to just turn into stone when it made contact but it just suddenly stopped. I successfully repeated this bug in a different world with creative mode and this time I placed the lava source block. Not too sure what causes this bug but i'm sure it has something to do with the new water mechanics/physics. I did find out that lava will turn to stone or cobblestone if is 1 block above the water before touching. If it is actually touching the water though, the bug will occur. If they are placed right next to each other, they will interact normally, so this bug only works in the Y direction if lava is on top.