Mobs that naturally spawn with equipment cannot have their equipment changed when spawned with jigsaw blocks.

When saving a structure containing an entity that naturally spawns with equipment (e.g. Skeleton), said entity will always spawn with their natural equipment during structure generation, even if its NBT is changed to different items.

How to reproduce:

• Summon a skeleton with any item other than a bow, for example an Iron Sword.

• Save it using a structure block.

• Create a Jigsaw structure using a data-pack, containing said entity.

Expected result:

• Structure generates a skeleton with an iron sword.

Actual result:

• Structure generates a skeleton with a bow, (its natural equipment) rather than the custom equipment.

Entities that do not naturally spawn with equipment can have it changed and generate properly. Spawning the saved entity using a structure block manually also spawns it correctly, with the custom equipment.