OK, next question. I've been reading and experimenting and learning how to use IDL for indoor scenes and have picked up a fair bit. I have run across a problem that I cannot figure out and have not been able to glean a solution from the threads I've already looked at, so... more questions.

Here's the scene with the light level that is ballpark to what I want;

now pretty much everything in view renders nicely except for the horrible splotchy walls facing the camera. I have tried everything I can think of to get rid of them, but that's difficult if I don't know why those materials and none of the others.

The lighting is 2 lights, one an infinite for the sun at around 800% and the other is a 'fill' point light in the middle of the room at 18% with shadows off. The light bloom on the wall between couches and TV is light leakage around the wall. I reduced the IDL IC to 20 but have kept the main IC between 50 and 90. IDL quality is maxed. I have tried changing the balance between the two lights but no real difference. IC adjustments gave the biggest improvements but not enough. In a fit of desperation I tried using box primitives to mask that wall and it has succeeeded in reducing both the bloom and the marks (see next) but not completely, and it seems a bit of a dodgy solution...

...so can anyone tell me what is really causing those marks? It's like the infinite light is 'burning through' the walls! BTW, I'm using Poser 2012.