When two "/fill" commands are executed in the same area in turn, the effect in the "bug1.png" diagram is produced. The correct result should be all lava.

How to reproduce:

1.Stand in a place and execute the command "fill ~ 10 ~ ~ 10 ~ ~ water" in the chat bar

2.Keep the same position as before and run the next command in the chat bar "/ fill ~ 10 ~ ~ 10 ~ ~ lava 0 replace water"

3.You can see an effect like "bug1.png" where all the water should be replaced with lava, not a grid

 
We hope Mojang can fix the bugs in the next version,Thanks.