Command NBT comparisons that include strings or numbers always fail

Testing for the presence of a compound or the emptiness of a list works as expected; testing for numerical or string values always fails. As such:

Always fail

@a[nbt={OnGround:1b}]
@e[type=item,nbt={Item:{id:"minecraft:stone"}}]

Work as expected

@a[nbt={}]
@a[nbt={Inventory:[]}]
@e[type=item,nbt={Item:{}}]
@e[nbt={ArmorItems:[{}]}]