I've noticed this a lot lately, on my last half dozen plans or so, and been meaning to ask...  But it seams like when I have a light "on" (with the "glow" showing) and I either adjust material, or turn another light on or off.. the glow disappears on the remaining "on" lights.  By no means a show stopper and RT still works showing the lights on.. but I like the idea of seeing which lights are on in advance.  The attached shows the same light and they both are on in the the 3D view.   Setting??