The bug

When you use bonemeal to a fungus (either crimson or warped) on few blocks below y=256 (eg. 253), they grow into huge fungus while tree saplings cannot grow in same condition, causing some of the weeping wines from huge crimson fungus to float in the air.

Steps to reproduce

Go to y=253 (or any height close to y=256)

Place a nylium

place a corresponding fungus on the nylium

Use bonemeal to it to make it grow

Observe how the weeping wines grow in the air

Use bonemeal to a normal sapling (eg. oak sapling) at the same height

The normal sapling won't grow into trees.