"MHF_" player heads except "MHF_Steve" and "MHF_Alex" still use old version textures(before 1.14) including
MHF_Blaze
MHF_CaveSpider
MHF_Chicken
MHF_Cow
MHF_Creeper
MHF_Enderman
MHF_Ghast
MHF_Golem
MHF_Herobrine
MHF_LavaSlime
MHF_MushroomCow
MHF_Ocelot
MHF_Pig
MHF_PigZombie
MHF_Sheep
MHF_Skeleton
MHF_Slime
MHF_Spider
MHF_Squid
MHF_Villager
MHF_WSkeleton
MHF_Zombie
MHF_Cactus
MHF_Cake
MHF_Chest
MHF_CoconutB
MHF_CoconutG
MHF_Melon
MHF_OakLog
MHF_Present1
MHF_Present2
MHF_Pumpkin
MHF_TNT
MHF_TNT2
MHF_ArrowUp
MHF_ArrowDown
MHF_ArrowLeft
MHF_ArrowRight

Besides, the bug may have probably appeared since 1.14