When theres a dispenser pointing to a moss block with stone (or other mossable blocks) underneath them, and then the dispenser uses bonemeal it doesn't spread it to the blocks below, unlike when using bonemeal with the player hand, where it does spread to stone beneath the moss.

Steps to reproduce
place a plane of stone with moss on top
place a dispenser facing into the moss
put bonemeal into the dispenser then power it

Expected result
the moss should spread to the stone below it (like what it does with the player)

Actual result
the moss's top gets bonemealed and doesn't spread

this is the case with both mosses