The bug

The mangrove trapdoor texture is highly symmetric and doesn't appear to have much of a defined handle. However, despite this, it still appears to point to the "orientable" trapdoor model template, meaning that the texture appears rotated depending on the block's facing direction.

How to fix

This could be fixed by having mangrove trapdoors point to the "normal" trapdoor template models like oak, dark oak and iron trapdoors do.

Alternatively, oak, dark oak and iron trapdoors could be made to rotate directionally like other trapdoors do and the "orientable" trapdoor model would become standard for all trapdoors.