Even if mobGriefing gamerule is set to false, if a silverfish enters mossy stone brick, cracked stone brick or chiseled stone brick, it will change its texture to regular stone brick's.
Possible solution: Add 3 new "Monster Egg" blocks with the textures of those three blocks OR disable entering to/exiting from stone-based blocks completely if said gamerule is set to false.

This is NOT a duplicate of https://mojang.atlassian.net/browse/MC-7134