BCC'd distribution lists cannot come before TO addresses without an error

When sending an email if the first recipient is a BCC to distribution list from the Address Book, and the second recipient is a TO followed by a valid address, then Postbox throws and error saying that the distribution list is not a valid address.

I have not tried other iterations of this problem. Fairly minor though since I just made sure that the TO went first and the BCC second, then everything worked appropriately.

Win XP SP3 Postbox 1.0