The rounded rect button type does not seem to exist anymore on iOS 7, being replaced instead with a square frame whose background color represents the entire frame, not just the area behind the rounded rect as it is in iOS 6.  The net effect is, when you set the background color of the button to clear, you don't see the button at all.

The easiest way to fix this was to implement a custom button that emulated the previous look, which will remain consistent in both iOS 6 and iOS 7.  All of the remaining changes, minus the preprocessor addition below, are for configuring the UI of the button.