The bug ...

I was smelting some ores, until I came up to some ingots smelting self.
I didn't take a snap shot until I found out how to do the glitch again.

Then I did it again, and it worked. It went the same with gold ore.
It was creepy, and cool at the same time. I found this out in multiplayer, Don't know if you might have it in singleplayer.

How to do the bug.
1. Make sure your in survival. ( I don't know if it works in Creative. )
2. Get your furnace and smelt some ores.
3. Right before the ore is done, Keep shift clicking the finished item box.
4. You will find that the ingot will be where the ore is supposed to be.

(UPDATE : The glitch was found to be a Lag Issue. The server does not use mods. It is vanilla.)