Modal QDialog created by application is hidden when application loses focus

Using Qt 5 on Macintosh, if an application creates and displays a modal dialog, and then the application loses focus, the modal dialog is hidden until the application regains focus. However, if the dialog is modeless, it is not hidden when the application loses focus.

Using Qt 4.8.3 on the same system, the dialog is not hidden when the application loses focus regardless of whether or not it is modal.

Steps to reproduce:
1. Build and execute attached project.
2. Click on the Modal Dialog button.
3. Select the window of another application (Qt Creator, for example), to deactivate the test application. The modal dialog created by the test application is hidden.
4. If the test application regains focus, the dialog is shown again, except that it will be shown under the QMainWindow created by the application.