Instead of having weird ass flickering lightning ingame, after following your steps it looks like this..
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This is how it looks ingame:
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I'm doing something very wrong i guess

Same in here Any solution??

Should we just wait until pcdev fixes this? Is there any way for us to do so (fix the issue)?

I found out how to fix this if you want to use your default_... SSIs like the default_day or somelike.

I wrote a text tutorial: here

This worked to fix the random lighting that is seeping through my walls but my enclosed room now has a random big shadow in the middle.

EDIT:
This is what my enclosed room looks like. I want it to be completely dark since its inside, the only light i would want is the one shining downwards.

But no matter what I do its like the sun light is going through the wall on half of the room.

Screenshot:

********************************************************************************
UNRECOVERABLE ERROR:
  LoadFx: no fxdef specified for fx placed in Radiant

Linker will now terminate.
********************************************************************************


Still cant fix this please help

Hey did you ever learn how to fix this?

Hey did you ever learn how to fix this?

It seems like its saying that you have an fx that isn't setup right. Make sure the fx path is valid and that its a working fx.

Changed decimal symbol... it worked, thanks xd

For everyone who is still looking for a solution.

Load a map in radiant then open the filter page (press F)

Above everything there are 3 boxes

- static probe view
- Game View
- Skybox

You need to tick the sky box