Beacons light beam is disappearing no matter if they are using stained glass blocks or just a beacon. By disappearing it is only at some angles. As you can tell usually in previous versions you can see the beam at all angles. Also when you are in the beam and looking up, you could see the beam continuing but now when you are in it all you can see is the sky. But no beam of light. It does the same thing on a 1.8.1 server/world as well.