Description:

Setting the world spawn beneath leaves will respawn the player on top of the leaves. In 1.12, leaves were ignored unless there was a solid block beneath them. Since /setworldspawn has been reverted to 1.12 behavior (see MC-245811 and MC-243079) this is inconsistent and can lead to issues (i.e. players being stuck on top of jungle trees). 

Steps to Reproduce:

1. Open a world in 1.18.1 and another in 1.12.2.
2. /setworldspawn beneath leaves (be it through /fill or a natural tree).
3. (Optional) /gamerule spawnRadius 0 to test same location. If larger than 0, /fill radius with layer of leaves.
4. /kill and respawn.
5. Player will respawn in 1.12 on the ground and in 1.18 on top of the leaves.

Recommendation:

Reopen MC-243079 and return 1.13 - 1.17 /setworldspawn behavior. By default this bug would be resolved.