I've noticed sometimes if someone has sent you two PMs since your last one and you use a .r command it will double send the message.
example:
Dude1: Hi
Dude2: Hows it going
Dude2: Wanna fly with me?
(Dude1 uses .r Sure, how bout 47s?)
Dude1: Sure, how bout 47s?
Dude1: Sure, how bout 47s?