Segue not calling prepareForSegue

Question

Perhaps I am missing something simple. I added a modal segue from a button to a view controller. I then added some steps to prepareForSegue (and checked I had named the segue correctly). I have done this a few other times with no problem.

Now, when I click the button, the modal window opens, but the prepareForSegue does not fire. I tried putting a log statement in the prepareForSegue before it even checks the description of the label (so theoretically it should fire for any segue). But I get nothing logged.

Any ideas?