Comment 2 for bug 1480138

That's likely not due to unity but the way the session works, the background is displayed by nautilus which is an application, and nautilus is closed before the session, also the scaling xsettings is set by unity-settings-daemon, which also exit before the setting close which might lead to the scaling factor to be unset and things to change on screen. Unsure it's easy to fix in the current session design...