For a comprehensive list of other examples of issues with 2D planes in models not being mirrored as expected, click here.
The bug
The planes composing glow lichen do not mirror on the back as one would expect, resulting in physical/illogical weirdness.
Fixed model (Mojang has full permission to use this fix):
[media]
How to reproduce
Place a glow lichen on a transparent block
View a specific flower on the glow lichen
View the exact same area of the glow lichen the flower was on on the direct opposite side
Note that the exact texture pattern at that position is different, even though it should be the same
Linked issues
relates to 2
Attachments
Comments

Can confirm.

Can confirm.
Can confirm in 21w05b.
Can confirm in 21w06a.
Can confirm in 21w11a.

The issue hasn't been fixed completely. Up & Down faces are still not mirrored correctly.
[media][media]