The bug

A dispenser filled with bone meal cannot create sea grass, however a dispenser facing a grass block can create grass.

How to reproduce

1. Run the following commands to create a setup

   /fill ~-1 ~ ~1 ~1 ~3 ~3 glass
   /setblock ~ ~1 ~2 dispenser[facing=up]{Items:[{Slot:1b,id:"bone_meal",Count:64b}]}
   /setblock ~ ~1 ~1 oak_button[face=wall,facing=north]
   /fill ~ ~2 ~2 ~ ~3 ~2 water
   

2. Press the button
   → No sea grass is created