my understanding is that the app needs to be rewritten using the ios9 sdk then it will multitask. the ios9 apps were just allowed to be added to the app storeiOS9 feels and works okay, but very disappointed with multitasking on an Air2 - only Apple apps get this special treatment. Additionally, if you have the YouTube app installed, Safari won't open youtube.com in the browser (so you could use multitasking to watch something). You must first delete the YouTube app. LAME.
Also some quirkiness with the auto-brightness - too bright, too dark... hmmm