Can't remove off-hand items by pressing F

Can't remove off-hand slot item by pressing F button. (Key bindings unchanged)
Tested in creative mode.
In the second picture, by pressing F, the item is duplicated.
In the third picture, by pressing G, the item is dropped and off-hand slot item displays 0 quantity.
In the last picture, F button can't remove the command block from off-hand slot.