Mobgriefing being off still allows creepers to destroy paintings. I tried many similar items and blocks and it seems to only be paintings.
Linked issues
Comments 3
Paintings, armour stands, leash knots etc can be damaged by mobs such as creepers, wither.
Mobs mentioned in MC-1673
creepers, withers, skeletons, strays, shulkers, ghasts and snowmen.
Paintings are entities. WAI i think