This may be related to MC-301993if the game tries to replace the default profile nbt with the value from the spawn egg, since the default would fail to be removed.
Can confirm in 25w37a
The profile nbt is either a mannequin profile or a profile component, meaning the model field does not exist when using the profile component format.
The wide/slim model is stored within the base64 properties itself and does indeed work when you use a resolved profile from a slim model.
Can confirm the CustomName entity tag is the only data copied to the copper statue block from the copper golem entity. The CustomName is copied into the entity_data component on the block instead of the custom_name component, and since the loot table does not specify any components to copy to the item, all of the data is lost upon mining the statue block too.
It would be expected that the custom_data component (the “data” entity tag) would be copied to the block, and that both the CustomName and “data” entity tags would be stored in the block as the actual components, rather than inside the entity_data component. This would also allow the loot table to preserve certain components, as the game does for other block entities.
It should be noted that when moving from 1.21.6 to 1.21.7 rc1 this is not a breaking change, but the pack format is meant to work both ways, and it is indeed a breaking change when trying a 1.21.7rc1 pack in 1.21.6, despite both updates sharing pack formats.
Can confirm in 1.21pre2. Also, when in creative mode, the items won't be able to stack immediately after unstacking. If you unstack the items in creative mode, then go into survival mode, the items that were unstacked in creative mode cannot be stacked in survival mode either.
I have confirmed it for 15w34a and 15w34b, but I'm not a mod so I can't mark it confirmed.
Can confirm in 26.2-snapshot-6