Calling QDialog::show() before showing parent window.

Documentation does not specify if it is supported to call show on dialogs before parent window is shown (which also can be a dialog). E.g:

main_window
dialog (main_window)
dialog2 (dialog)

dialog2.show
dialog.show
main_window.show

On X11 this at least does not seem to be supported by tested window managers. Note: I did not test very thoroughly.

Is it a programming mistake to call show() in this order?