Signal/Slot Editor Not Usuable on Mac OS X

If I create some widgets in Designer, and I open the Signal/Slot Editor, I am able to use + to create new rows. However, with a double-click on <sender>, a combo box with "<object>" object appears, but no items drop down to choose. Clicking on "<object>" only causes the space to revert to <sender>. I also notice that the combo box is smaller than usual – smaller than in Qt 4.8.x. And I checked in Designer for Qt 4.8.x, and this functionality did work correctly.

I am including a snapshot of the Signal/Slot Editor. I wasn't able to catch it at the point where the tiny combo box appears.