Can't get Qt App to look same under Windows and Linux - Need help

[FToe]

I have an Qt application that has a main window with dialogs that pop up full screen. Each dialog can pop up other full screen dialogs that cover up the preceding dialogs. Closing a dialog returns to the dialog that was hidden underneath it.

This works really nicely under Windows.

When I compile it for Linux the dialog boxes stack one below the other with the title bar of the previous dialog visible. (See attached image) I want each dialog to hide the previous ones, like they do under Window Qt.

Why is this behavior different under Linux? How can I make this work? I am using running under Ubuntu Linux

Thanks