It bugs when I have a contact's birthday stored and saved, and when I sync the contact with another platform (i.e. Facebook) and that person left out the year in their bday (a lot do this for many obvious reasons), the phone OS or the People Hub isn't smart enough to recognize they are the same and aggregate this date or combine them. Instead, I get two separate birthdays for the one contact, one showing from my outlook and another from facebook or linked in without the year. Its a small nit but an annoying one.
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