If a player right clicks on the output of a furnace, the player receives half of the items in that stack, and a FurnaceExtractEvent fires. However after this happens, the next click on the same furnace output does not cause any event to fire unless the furnace has updated the output by burning more items.

To reproduce:

1. Install attached plugin
2. Log in a player
3. Make a furnace
4. Smelt two cobblestone to stone
5. Right click the furnace output to pick up one stone
6. Notice the log message on the console
7. Right or left click the remaining furnace output to remove it
8. Notice no message is logged, because the event did not fire

If you smelt 3 items, and remove one of them after the second completes smelting, then remove the remaining 2 after the third completes smelting, both events fire. Something strange occurs after right clicking the furnace output though. It does not matter if you close the furnace window and reopen it.