All the birthdays on my Rezound's Calendar were showing up twice, with no way to delete one of them. An extensive Google search found the most common solution was to sign out of Google on the phone, and then sign in again. I was afraid that doing so would cause me to lose all my assigned ringtones, so I held off. Then I got brave and tried it on my Xoom (which had the same double birthday problem on its Calendar). It worked, and all seemed well. So I removed my Google account from the Rezound, and re-activated it. Yep, that fixed the double birthday problem and created a batch of new issues. All my phone contacts and Google contacts became unlinked, so I had to go through all 146 duplicates and re-link them. I had a panel of Favorites, and when I touched the icon, I got an error message stating "Invalid number". Jeeze, I really hate it when the error message is a damn lie. After a lot of hair-pulling, I found that it wasn't an invalid number, the function of the icon had to be re-established. It didn't occur if a person had only one number on their account, but if more than one, I had to re-select which number I wanted to call when I touched their icon.
My wife's Dinc 4G had the same double birthday issue on her calendar, and removing and re-establishing her Google account created the same problems as it did on my Rezound, and additionally she lost all her ringtone assignments, having them all go to default.
Time will tell if more problems crop up as a result of the Google account reset. If anyone knows of an easier way to fix the double birthday calendar problem, please let us know.