Never receive MouseButtonRelease event when clicking on "title bar" of QDialog

I'm trying to implement a special drag-and-drop type behavior with QDialog. I want the drop action to take place when the user releases the mouse. When clicking in the title bar area of the QDialog I'm getting a QEvent::NonClientAreaMouseButtonPress, but I never get the corresponding QEvent::NonClientAreaMouseButtonRelease.

Does anyone know how to receive MouseButtonRelease events when the user clicks in the title bar area of a QDialog?

Relevant code is attached.

Thanks!
Scott