Mangrove leaves are anisotropic (i.e. do not have random rotation) on the top and bottom, as compared to all other leaf types, which have isotropy on the top and bottom. This is seen in the below image:

To make it clearer, here is a video of the same thing but the leaves are waving, helping to highlight the anisotropy: mangrove_leaves_anisotropy_waving.mp4

How to reproduce:

• Place down all leaf types in small rows
• Observe the random rotation of the leaves on the top or bottom faces

Expected result:

• All leaf variants are randomly rotated (isotropic) on the top and bottom faces

Observed result:

• Mangrove leaves are anisotropic on the top and bottom faces. All other leaf variants are isotropic.

How to fix:

• In blocks.json in the vanilla resource pack, add

"isotropic" : {
   "down" : true,
   "up" : true
} 

to mangrove_leaves