with no items filling the inventory, the bucket teleports to the top-left most slot instead of being picked up. bypassing this with filling everything with items reproduces this bug.
tested on client with nothing but agricraft and fastcraft. reproducable.
http://imgur.com/gallery/ELNNc

Has been fixed, but there hasn't been a new release with this fix: InfinityRaider@6a0c5e2

Also see #629