Why do I have duplicate contact birthdays on Android calendar?
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TomSawyer_2112

Hey Guys,

I had to clear the Calendar Data for the Bday to show on my calendar. This is what I did,
Go to Settings-Applications-Manage applications, then select Calendar Storage then "delete data". After doing this the screen (HTC EVO) will reboot (white screen with the HTC Logo).

After clearing the data, go to the calendar setting and add the Bbay.

Hope this work for you.
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Source:
http://www.google.com/support/forum/p/android/thread?tid=58d284f1a1f36866&amp;hl=en