Glow Lichens can spawn on air and not on blocks.

Sometimes Glow Lichens can spawn on air and not on blocks. 

This happens when two Glow Lichens are connected and one spawns on a block and the other spawns in the air, although this can definitely happen when they aren't connected but just actually floating in mid air.

Recently I found out that this bug can occur in caves and not just underground structures like mineshafts and strongholds. Unfortunately I was unable to get a screenshot of this bug occurring in caves and not in underground structures.

I have attached images.