In GNOME 3 when displaying any QDialog it appears that it can't be moved and it has no title bar.
Is there a way to re-enable the title bar and make it movable? I attempted to use a QMainWindow as a workaround instead but it appears in the task bar and won't appear as a "modal" dialog.
Probably, it might help you:
Type r in Alt+F2 prompt to restart Gnome shell and see the changes (QDialogs should become movable).