Duplication Glitch

The new Classic UI for touch devices brought a new duplication glitch. I'm not 100% sure about how it works, but I smelt a full stack of iron. My inventory was full, and I already had one ingot in my inventory. When I moved the stack to the ingot slot, it duplicated. Both my slot AND the furnace had the stack.

Here's another situation:

Later, I smelt 10 ores with the inventory full, and I already had 56 iron ingots in my inventory. It didn't duplicate, but I was able to make infinite XP.

I use a Samsung Galaxy J5 2016

Sorry if I mispelled something, I'm trying my best to speak english correctly...
(Some players will be mad at me for reporting this glitch, but... I don't care :v)