If you place a stone furnace on top of another stone furnace while it is smelting, it plays the building placement animation. Clicking and dragging results in repeated animations.
Same for steel furnaces.
[0.11.3][kovarex] Furnace infinite building animation
Re: [0.11.3][kovarex] Furnace infinite building animation
Thanks for the notice, it is fixed for 0.11.4 now.