When you cancel the InventoryMoveItemEvent caused by a Hopper for one item (e.g. the one in the first slot) it will not move on to an item in a slot after it (like it would in Vanilla when the target container doesn't have a slot were the item fits) but it stops the moving completely.

This seems to be due to the return of false here in the TileEntityHopper.patch. With a continue there it could result in a more Vanilla-like behaviour.

I don't believe that this was intended behaviour when the event was implemented and if so I propose to change it as it would add more functionality to the event to make plugin mechanics that better match the Vanilla behaviour.