I place an oven. Below I place a hopper to direct finished items into a chest. The stove burns raw gold ore to gold.

To save coal, I use Shift + Click (as fast as I can click) to instantly inject iron ore when all the gold ore has been consumed and diverted into the chest.

However, unlike expected, a last block of gold in the oven remained as input. At the same time, the stack of iron ore remained in the player's inventory. The stove worked visibly (progress indicator), but nothing else changed. Neither the one block of Gold ore nor the stack of iron ore disappeared.
Only when I closed the oven and reopened, the display was updated correctly. The gold ore had disappeared, the iron ore sat in the input of the furnace, and had already been partly processed. Finished iron was already found in the chest.

Diagnostics: It actually works, but the GUI of the oven is not updated correctly (might be a display or network update error since this all happened on a localhost vanilla server!?)