If I right-click an armor in a non-standard chest, backpack, crate. The item in the armor is replaced with the item clicked but is not removed from the container. The item in the armor slot is removed and not moved to the container or inventory. If I keep right-clicking on the armor that is still in the container, it will then start duplicating the armor in inventory. I have seen it happen with Barrels and Crates from charm mod, the variant chests from quark, and backpacks from the Useful Backpacks mod.

Logs Part 1: https://pastebin.com/raw/YJeWk34B
Logs Part 2: https://pastebin.com/raw/2iaTiQHj