The bug

It seems that the top of water doesn't get rendered if there is transparent block (this also includes slabs for example) in a 1 block radius one block higher than the water. This makes water look pretty strange if it is tilted.

How to reproduce (general steps)

1. Fill a 3 x 4 area of a solid block like stone
2. Place water or lava below middle block at the edge of a 3 blocks side
3. Move inside the lava or water block and rotate in the direction of the area you filled

How to reproduce (commands)

Use the following commands without moving

1. Optional to make sure the water or lava block does not move you

   /gamemode spectator
   

2. /tp ~ ~ ~ 0 0
   

3. /fill ~-1 ~2 ~ ~1 ~2 ~3 stone
   

4. /setblock ~ ~1 ~ water