Can't summoning different variants of some mobs in command

When summoning different variants of dogs(wolves) and cats, the alphabet "v" of NBT "variant" in command，MUST lowercase "v",otherwise capital "V" ONLY spawns default variety.
For example 
/summon minecraft:wolf ~ ~ {variant:black,NoAI:1,NoGravity:1,Silent:0,PersistenceRequired:1,Invulnerable:1,Owner:bruh}
spawns black wolf.
Otherwise
/summon minecraft:wolf ~ ~ ~ {Variant:black,NoAI:1,NoGravity:1,Silent:0,PersistenceRequired:1,Invulnerable:1,Owner:bruh}
STILL spawns default white wolf.
However parrots and other mobs not found this bug.

The version 1.21 has already had the bug.