手机休眠/锁定时，UIAlertViewDelegate方法didDismissWithButtonIndex被调用

I have a UIAlertView who's didDismissWithButtonIndex delegate method calls pops the view controller (same class, it's the alertview delegate and the viewcontroller) to return the user to the previous screen. The issue is that when you lock the phone before the [alert show]; is called, I have a UIAlertView who's didDismissWithButton