When breaking a bloc, the furnace interface appears on it. I suppose it appears only at a specific step of the breaking animation, I think it's the second step, because it doesn't appear immediately when starting breaking the block, and it disappears when the animation progresses; it satys more or less longer depending of how long it takes to break the block, for exemple it stays almost 1 second when breaking cobblestone with hands.

The interface appears on every sides of the block, and it seems to appear on every blocs, I tried on full blocks, stairs, slabs, glass, even bamboo, chains, lanterns. 

I have no idea how to replicate this bug. 

edit : I just realized it could be smoker or blact furnace interface, I don't know if it makes a difference, but I think the bug appeared not long I started using them for the first time.