Not possible to show windowmodal QFileDialog after showing other windowmodal dialog

After showing a window modal dialog (=sheet) on an application modal window, a subsequent attempt to show a window modal file browser doesn't work (the file browser is never shown).

I've created a small test program to reproduce the issue:

• click the "Modal" button.
• Click the cancel button in the shown sheet.
• Click the browse button 

A file dialog should appear but doesn't. Showing an application modal file dialog works.