No, normal site but it looks like it's connected with the device orientation, ie. detected screen width.
Tablet in portrait mode it doesn't show up, (1200px), but in landscape it does, (1920px).
Same with the phone, 1080x2400px.
Never noticed it because I rarely go to landscape mode due to if I ever have to type anything 85% of the display gets obliterated by the keyboard so I find myself scrolling up/down in the remaining 15% to see what I'm referring to, add markdown, etc, etc.
Be nice if you could customise what's in the top header box in some way, ie. I don't really need the Profile, Search, Go To... links.
I'll change the topic subject.
Btw, what is the screen width at which point it starts removing objects if someone knows?