The bug
Although glow lichen can be placed on the side of a block of snow, they cannot be placed on the side of 8 snow layers.
How to reproduce
Get 8 layers of snow by placing snow on top of each other
Attempt to place glow lichen on the side of it
❌ The glow lichen cannot be placed on the side of the snow layers, and if there is a block below where you are attempting to place it, it will be placed there instead
Attachments
Comments 13
Can confirm in 1.17.1 Pre-release 1. They also cannot be placed at the top, but they can on snow blocks.
Can confirm in 21w08a.