Starting wth RC1, when moving items from active bar to inventory or from inventory to chest, it doesn't always move.  For example, moving several buckets from inventory to chest, I start to shift click.  The first one or two move fine but subsequent moves require me to move the pointer off of the item and back on.  I've had this happen on two different systems with different mouse configurations (one wireless; one wired).  I have experienced other mouse clicks not taking but it is most noticeable during inventory moves.