Screen flickers when app is moving to background

I create blank Unity project and run it in my iOS devices. Each time I'm moving my app to background (clicking twice home button) screen of my app blinks a while (Full Video). I've recorded it, slow down video playback and find out that in the middle of moving process system makes screenshot, show it and switch back to app screen (Slow Play Video). Is this a bug? Or I need to do something to fix this?