It isn't just the NPC's mate! Watch your own toon. Whenever you fill a straight or a flush, your toon does the same thing. This means that if you are playing with real live players, you are giving away your hand! I sent in a bug report on this btw.
__________________
Sir Upticious
Current Open Pirate: Purser Veerant
Current Test Pirate: Dog Greenhound
Owner of Green Mongrel
Scourge of the mediocre seas!