Just like fences and walls, grass does not grow under hoppers and cauldrons.
How to reproduce:
1. Put a hopper or cauldron over a grass block
2. watch it turn to dirt like if it was a normal block
Note 5
Linked issues
is duplicated by 1
Comments 6
Fixed in 0.15.0 (Tested in Windows 10.) None of these blocks cause grass to turn into dirt. However, they still prevent it from growing there if the block was already dirt. See MCPE-7848, which covers grass not growing under blocks.
Confirmed in 0.14.0 alpha. Glass and redstone dust prevent growth of grass too. It is possible that all of transparent blocks have the same problem.