FOSS gamedev and creative worlds

There is a setup which one can use to reproduce this bug.

First, create a pool with a column:

8 blocks wide, two blocks high, with three blocks high 2x2 column in the center.

Then put two (or four) lava blocks on top of the column.
Wait for the stable flow.
Put two blocks of something on top like it is shown on the picture:

Black tile appears.

i get that when i dig pitfalls or some times trees turn black usual if you leave it alone it will turn normal

I could reproduce this with the same setup using the current master (554f7f120c). Good work. I hope this finding will lead to a fix.