Azalea tree generate on top of bamboo

What I expected to happen was...:
Azalea tree in theory generate on top of dirt or grass block

What actually happened was...:
Azalea tree appear on top of bamboo and the rooted dirt is below bamboo

Steps to Reproduce:
1. create a normal map with this seed (27905854)

2. go to this coordonate (tp @s 265 87 148)