[BUG] 2.43 Windows - Ray of light / Opacity / alphashadow???

[Synthercat]

I was testing one of my favorite scenes and found a light bug

Here is how the scene really is :
NOTE : pathtracing kernel
FILE COMMENT : 1st Scene

I use the same material for glass through the entire scene.... so what I try then (to check if I can vanish some items)
Is to make most materials Opacity=0... now even the 0.5cm windows is Opacity=0
Special note : alphashadows is set to OFF (it matters, you'll see soon)
Here is the scene :
FILE COMMENT : Glass material in now Opacity = 0

Then I switch to directlighting the scene begins and I switch to path a few seconds later... I am in shock with the result :
FILE COMMENT : WOW Check that rays!
PS It took me hours of testing to figure out what was going on!!! Here it is : Changing the kernel back n forth resets it to some defaults. It was the alphashadown ON that did the trick and I have no idea why (although I am not sure what the alphashadow does exactly I am pretty sure that's not what it's there for)

Here is the super-weird part : In order to ruin that rays and make it as it was in the 1st Scene you can do 2 things that will have the same result :
Change alphashadow to UNTICKED or... Change Glass Opacity back to 1!!!
FILE COMMENT : Glass Opacity back to 1

Analysis : The only way to have these bright rays in the room is a) To have alphashadows TICKED and to NOT have glass opacity set to 1 but have it something like from 0 to 0.6. Isn't this "wrong" I mean in real life wouldn't these ray pass through the glass (I USED IOR = 1.5) and hit the floor?

[kubo]

If I have understood you correctly this IS how it should work. The thing is that right now light passes thru alpha mapped materials (opacity of certain areas different from 1) in pathtracing with the alphamaps bool on, but it doesn't go thru specular materials just yet (we'll have to wait for a future built for that, abstrax dixit). For now a trick that someone found (not sure if proupin) is that if you modify the materials opacity to something lower than 1 then light passes thru. Althou at least in my test I would not go as far as 0 'cause that's actually as if it wasn't there yet it's being calculated, so If you want to use 0 just hide that object and untick the alphamaps your render will be faster and you won't see a difference, or if you want light thru and reflections (like in glass) set something like 0.5 and the such.