Brewing Stand stops brewing when half stack is removed from input slot

To reproduce in 15w36d:

Place brewing stand, add 2+ items to the input slot and attempt to remove half with right click.

GUI shows that brewing has stopped. With the GUI still open, a single left click of the items in the input slot will return it to the inventory.

If the GUI is closed with the non-brewing items in the input slot, those items will either disappear from the brewing stand, or be returned to the inventory.

http://zippy.gfycat.com/ShowyOrneryBobwhite.webm