Structure blocks loading mobs can give them additional equipment

The bug

When a mob like a zombie is saved then loaded as a structure, sometimes it will gain or replace armor or weapons, as if it were a natural spawn and not a presaved entity.

How to reproduce

1. Download the attached world
2. Pull the lever, triggering the structure block to load the zombie wearing a leather helmet repeatedly
→ Most of them only have leather helmets
→ Some of them have different armor, or new weapons