When I use the mouse to open the furnace UI and my cursor happens to already be over the output slot, it does not switch the active slot (the one colored in green) to that output slot unless I move my mouse by at least a pixel. This is deceiving because if I click on the slot my cursor is on, it actually clicks on the input slot.

I would expect the UI to detect immediately where the cursor is and activate the correct slot instead of waiting for the mouse to move.