Recently updated my iPhone 4 to iOS 6. A person's birthday showed up twice, then 3x, 4x, now 6x in my calendar. I can't delete any of them and they keep multiplying.
I enabled Facebook integration when I updated to iOS 6.
I am not using iCloud. iCloud Contacts and Calendars sync are off.
My calendar syncs to gMail.
If I go to my Google calendar online, the birthday shows up only once.
4x duplicate birthdays: Calendar - my gmail account. Accepted: Contacts
2x Calendar - my gmail account
All of the duplicate events have the same note "Today is Jane Doe's birthday!"
The "correct" birthday comes from the iPhone contact.
Capitalization of the events are slightly different. With the one from the iPhone contact, it reads like "Jane Doe's Birthday". All of the duplicates have a lower-case "b" - "Jane Doe's birthday".
At first I thought it might have something to do with FB integration, but one person's birthday is listed 6x whose info is only in my iPhone contacts - he doesn't have a FB account. Oddly enough, people who I'm FB friends with, but didn't have an iPhone contact for before iOS6, their birthdays only show up once.
Here's what I did:
1. Go to http://www.google.com/calendar/iphoneselect and deselect all calendars.
2. Go to your iPhone calendar, select calendars at the top right and deselect all calendars.
3. Go to Settings>Mail, Contacts, Calendars>and then either GMail or Exchange (whichever you have enabled your calendar through.
4. Now turn off your calendar. You'll get a warning that everything will be deleted, but that's ok.
5. Now go back to the Google web page and select the calendars that you want to sync but don't select either of the ones to do with birthdays listed under Shared Calendars as your iPhone will generate these anyway.
6. Go back to your calender account settings on iPhone and turn calendar back on again.
7. Go back to your calendars on iPhone and select which ones you want to sync.
Et voila..........crazy duplicate birthdays gone :-)