Hi. If I understand it correct, this is part of the the same problem as I have had recently. There is only a small difference in my setup vs. DotDesigns: In my case I've made a dedicated "Lightselect_Environment" RE, where I believe DotDesign are refering to the automatically generated "Rest (unassigned" RE) when he says "Lightselect Environment Channel.
The problem I've found is, that when "visible directly" is checked in a Corona light, the directly visible light is part of the "Rest" RE and NOT the Lightselect RE for that light (pic. 1).
However when making the same setup for an object with Corona Light Mtl applied to it, the directly visible light is part of the Lightselect RE for the object/light - just as expected (pic. 2).
But - If "Emit Light" is turned off in the Corona Light Mtl, then the directly visible light suddenly is part of the "Rest" RE (pic. 3).
This behavior makes it difficult/impossible to turn off a single light in the lightmixer, in situations where the light is seen directly.
Hope my explanation makes sense. I've attached 3 pictures to make it understandable.
Regards
NB - the test is made with 3dsMaxDesign2014 and Corona 1.6 DB Mar 27