Comment 6 for bug 1577641

Unity8 needs this bug fixing for one simple reason:
Even apps that do display a window "immediately" will get a splash screen of the wrong size displayed before a window of the correct size appears. This will be particularly important after bug 1606501 gets fully fixed.

And no, it's not invalid for Xmir to not create a window on start-up in rootless mode, it is correct behaviour. It's a server and has no windows until the X client creates one. It's distracting and confusing for Unity8 to create a black window where there should be no window at all.