Comment 4 for bug 1532974

This is a very old issue.
On surface creation a mir callback is called where qtmir can modify the parameters of a surface about to be created, such as its size. Gerry tried in the past to connect this callback to unity8 so the latter could set the size properly, but it led to some horrible threading-related crashes and thus pulled out.

If I'm not mistaken nowadays that callback (MirWindowManagerImpl::add_surface I tink) simply defaults to the screen size, which is a fine default for phone but evidently not for desktop.

And this old issue was made more evident now that we no longer stretch windows in shell, so on desktop you see a fullscreen window for a splitsecond before the app responds to the resize.