Birthday calendar bizarre repetitions and other issues

Question

I have the STRANGEST things happening with birthdays on both my iPhone (5, 32GB, white, iOS 6) and iPad (32GB, iOS 6, white).
I'm posting it here in the iPhone forum, assuming more people may be able to help.
First of all, I sync a Google Apps calendar with my iPhone and iPad via CalDAV. I also sync my Google Contacts with my address book (including birthdays), which syncs via my MacBook on OS 10.6.8 using the sync icon in the system tray. (I hesitate to call it MobileMe, even though that's what the System Preferences calls it, because it really has nothing to do with MobileMe -- it does not sync via MobileMe [I do not have an account], it just syncs my Address Book with Google with my phone or iPad when hooked up. It is through a WIRED connection that it does the final sync to the device.)
So, my birthdays from my address/contact books and my Google contacts DO sync and they DO show up on both my iOS devices in the fancy Birthday calendar with the cute cake symbol, as well as in my Google calendar.
NOW HERE'S THE CRAZY PARTS.
Sometime recently, my birthdays were getting repeated. But oddly, enough they are a different amount on the two iOS devices. I have 18 copies of all birthdays (on the same day) in my iPhone calendar and 68 (YES, SIXTY-EIGHT COPIES) in my iPad of every birthday.
My Google calendar shows NO SUCH ERRONEOUS copies.
The crazier thing is that the copies of the birthdays are NOT on the birthday calendar. In fact, IT'S AS IF THEY JUMP AROUND ON DIFFERENT CALENDARS. They show up all one color, but some random color. They will appear or disappear only SOMETIMES if I turn "off" some calendars or others (for example, once they would go away if I hid a "Personal" calendar, another if I hid a calendar I subscribe to via Google but sync via CalDAV from Weather Underground, and another calendar that is a Google calendar but also my "default calendar" in the iOS settings). And this is all within minutes.
When I go into an instance of the repeated calendar event, it will actually say it belongs to my default calendar, regardless of what was hiding or showing it before.
When I try to "edit" the birthday just to see what happens, it crashes the app.
WHAT. THE. ______???
Here's what already I've tried:
Searching the internet for someone with a similar problem. NADA.
Turning off the option to sync my Google birthday calendar via the Google sync page (I think it's actually unnecessary anyway, since iOS pulls from the contact book, anyway). That did nothing.
Hiding all calendars and then selecting them to show one at a time to figure out which calendar was causing the problem, but as I mentioned above, it is not consistent.
Re-syncing my devices with iTunes.
Searching for and merging duplicate contacts in Google contacts.
Turning off the iOS birthday calendar.
Killing and re-starting the calendar app.
Re-starting my iOS devices.
Re-syncing my contact book with my devices.
Someone. Please. Tell me you're having this problem and that you have the solution? I'm going crazy over here! I can't remember anything that may have triggered this to happen.

Answer 1

I figured it out! (Or at least, it's been fixed for a day on both my iPad and iPhone.)
By the way, I discovered more oddities, but I'm not going to even bother with describing them.)
I am assuming everyone here has been syncing their birthday calendar off of Google/Gmail (whether CalDAV or Exchange, it doesn't matter).
The key to this is to know three things:
A) Tgara was on to something: syncing the Google birthday calendar in your Google sync settings -- even though it does not show up in your calendar list on the iphone/ipad -- is the culprit.
B) BUT, simply un-syncing will not make them go away unless you completely un-sync all your Google calendars. Once the repetitions get into your phone/iPad via they are kind of "stuck" there, and you've got to go back to the beginning to un-stick them for good.
C) Thus, it may require some trial and error because I had to repeat this a couple times. I may no have the right order of operations, but this is my best recreation/guess.
How I fixed it (I had to repeat a couple times for some reason):
1) I'm debating whether you have to do this step (I think I did it on my iPhone, but not my iPad, and yet both worked), but it doesn't take long, so you could just to be safe: on your iOS device, Settings > Mail, Contacts, Calendars -- delete your Google calendar account.
2) On your iOS device, go to the proper Google sync page to choose what calendars are available for syncing.
For Exchange, go to: https://m.google.com/sync/settings/iconfig/device
For CalDAV and Gmail/normal sync, go to: https://www.google.com/calendar/b/0/iphoneselect
For Google Apps CalDAV (although it worked for me on the normal page above), go to: https://www.google.com/calendar/hosted/yourhosteddomain.com/iphoneselect
If you're not sure which method you use, do both of them.
3) Sign in and choose the device in question (if prompted) and then uncheck ALL the calendars. Save/apply.
4) Go to calendar app. You should have an On my iPhone or On my iPad calendar and the iOS birthday calendar. Ensure that no repetitions are seen when you check mark each calendar idividually and also collectively to be visible. If there are, repeat the steps above.
5) Once the repetitions are gone, go to your iOS settings and add the calendar account back in if you removed it in step one.
6) Go back to the calendar app. Again, you will have two calendars -- one default Google calendar and one ios birthday calendar. Turn on each one at a time and also together to make sure the repetitions are gone. If they are not, repeat the above again.
7) Once they are gone, go back to the Google sync page(s) and add all the calendars you want back, BUT DO NOT SELECT YOUR BIRTHDAY CALENDAR. Save/apply.
8) Go to the calendar app. Open up the calendar list. Wait for it to refresh. Now you should be able to turn on all your calendars you wish to see, wait for it to propagate, and confirm there are no copies. If there are copies, repeat all the steps!
YOU DO NOT need to erase your contacts. Not sure about iGust's work-around, but that's unnecessary. And christina44, I actually think this is a different problem. All my copies were on the correct date.