Why is my app dying after invoking popToRootViewControllerAnimated?

Question

After I call

[self.navigationController popToRootViewControllerAnimated:YES];

I can see in the root view controller that viewWillAppear enters and exits.

Then I see a message on the console that reads

*** -[CFString release]: message sent to deallocated instance 0x4a9eab0

And then my app abruptly terminates.

I don't think it's in any of my methods when this occurs.

Note that before I pop to the root controller I have the code put up an alarm and I can see the root view underneath the alarm and as soon as I press the "cancel" button, my root view disappears and the iphone simulator displays the home page instead of leaving my root view showing.