Blank NSComboBox on OS X Yosemite

Question

I have a set of NSComboBox elements shown within the toolbar of an NSPanel, all created with XCode/Interface Builder. When I click on them on Yosemite, all I can see is a black box where the combo box items should be. On earlier versions of OS X this works just fine. No exceptions are logged at all. Here's a screen capture:

Any idea of what could be broken? I can't see any relevant release notes from Apple.

Answer 1

Bypassed this by using a NSPopup instead.