Minecraft Version: 1.16.3
Forge Version: 34.1.42
Mod Version: 0.11.1.81
The Auto smelt is dragging my (modded) Ores into the slot to burn them.
This dupes them to a full stack.

There is no complicated things needed to reproduce this bug, just let your ore smelt and enjoy

Thanks for reporting this. Fairly trivial omission which I got fixed in the new version on curseforge.