The current behaviour is without a doubt intended as per MC-96463 (refer to ticket's history) and the Works As Intended resolutions of MC-199241, MC-199248, MC-202595, MC-202598 and MC-206570. Please focus on fixing all other currently open plane-mirroring tickets.
Note how the targeted leaf section does not appear in the same place on the back of that plane.
Fixed model attached.
Linked issues
relates to 4
MC-202598
Seagrass textures are not correctly mirrored from behind
Reopened
MC-199237
Back of ladder is incorrectly mirrored
Resolved
MC-199239
Vines appear incorrectly mirrored when viewed from behind
Resolved
MC-199241
Texture planes of cross models appear incorrectly mirrored from behind
Resolved
Confirmed for 1.16.3