Gamerule MobGriefing does not toggle Sheep's grass eating behavior

By turning gamerule mobGriefing to false, I expected to see either :
_Sheeps still performing the eating animation while leaving grass and tallgrass untouched
_Sheeps no longer performing the eating animation (and thus, never grow wool back)

What actually happened :
Sheeps still perform the eating animation and destroy grass and tallgrass in the process