I've just upgraded to 8.12 Community, and when clicking the “Maximize” button it leaves a gap the height of the title bar at the top of the page.
No other applications do this, and it wasn't doing it on 8.11, so I presume a minor issue has crept in.
BTW, I've not restarted since upgrading from 8.11 to 8.12, so I'm not sure if this is something that will be fixed with a reboot – I'll try at lunchtime and if it fixes it I'll post again on here.
I'll post a screen shot of how my Windows looks with no other apps open after the reboot.