Presently leaves do not update the world around them when they decay due to having their tree removed.

The best example being when there is snow on top of a tree. If you break the leaves manually the snow will be removed, were as if you remove the trunk of the tree and let the tree decay then the snow will stay in place.

Wow. That's an odd one.

Is leaf decay actually something in EBXL, or is that in normal vanilla code; is this something for EBXL to fix, or for forge to fix?

...

Gotta see if I can make a "sand castle" using this...

It actually originates from vanilla code which has been updated since EbXL copied it back in the day. It was implemented differently depending on which type of leaves were decaying. Autumn wood leaves would do a "world.setBlock(x, y, z, 0);" while the green leaves such as the fir and the redwood leaves did "world.setBlock(x, y, z, 0, 0, 0x02);"

In the modern code the vanilla does "world.setBlockToAir(x, y, z);" which the surrounding blocks so that is what we will be doing here.