While in my redstone testing world I noticed the sheep in my shearing-machine was playing the animation for eating the grass however the grass stayed grass and didnt turn to dirt. 

To test it further I put a few sheep in a fence post pen and watched as the sheared sheep ate the grass, became shearable again, and once again the grass didnt change.

I hope that in one of your next bug-fix updates you check and see if an error has occured in the grass mechanics. I currently play on xbox one, 1.17.11 .