So with the update to the explosive barrels and only being able to carry one stack in your inventory comes a new issue.
Last night I tried to move some barrels, ended up encumbered so went to split my stack back into the storage box. However I let go of the mouse whilst still hovering over inventory and the split stack disappeared. I tried it again by moving one out of the stack again and that also disappeared.
So be warned guys, only place what you can carry in your inventory or risk losing them.