It is about the furnace glitch, read discription

I was on my survival world when I put 2 logs into my furnace
On the top slot then tried tapping the bottem slot many times but
it wouldn't activate.
Then I tried taking my logs back but they wouldn't go back
So I had to destroy the furnace.

To activate the bug place a furnace and open it.
The bug is always active in version 0.7.0