Diamond chestplate turned into iron chestplate when placed in an item frame

I had a problem placing an enchanted diamond bib in a frame, I had a diamond bib with thorns and protection against projectiles in my inventory and I wanted to place it in the frame and at the time of putting it on it became an iron bib without enchantments, when I removed it from the frame and fell into my inventory it became an iron bib,  I lost my enchantments and my diamond breastplate