summary

"!" operator used outside of the root components field displays inconsistent behavior with its use in the root components field

steps to reproduce

1. run command: 

/give @s amethyst_shard[custom_data={"some_custom_data":{}}] 

2. hold the amethyst shard in your main hand

3. run command:

/item modify entity @s weapon.mainhand [{"function":"minecraft:set_components","components":{"minecraft:custom_data":{"!some_custom_data":{}}}}] 

4. run command:

/data get entity @s SelectedItem 

expected result

item's "custom data" field should either:

• be empty, if "!" operator is permitted inside of another component
• contain both "some_custom_data" and "!some_custom_data" if operator is not permitted inside of another component

actual result

item's "custom data" field contains only "!some_custom_data", as if the relevant tag were removed, but the tag signalling to remove that tag were also added.