Sheep eating grass doesn't turn grass into dirt

Sheep grass eating animation happens, and sheered sheep regain their wool after the animation, but the grass doesn’t turn into dirt.

In principle it’s OK, but this broke the common wool farm with an observer sending a signal to a dispenser with sheers as soon as it detects the grass changing into dirt.

Edit: Silly me, I had mob griefing off! Sorry! This can be deleted!