PKPassLibrary - Remove a pass

I am using the PKPassLibrary to add a pass to Passbook, which is working fine. But removing a pass from Passbook is silently failing. I am calling PKPassLibrary.Remove.

To add a pass I am using

var pk = new PKAddPassesViewController(newPass);
navigationController.PresentModalViewController(pk, true);

To remove a pass I am using

library.Remove(pass);

Should remove work? Is there something I am missing?