CPU BiDir broken or changed somehow?

[FarbigeWelt]

Look at this post and its animated gifs.
Lenses, CPU BiDir, different depths
Now look at this 'pale' image.
Lenses, CPU BiDir, depth 25
What is going on here

Gems.zip

(879.76 KiB) Downloaded 136 times

[Fox]

You by mistake set the air ior to absorption slot, so it was at 1.5 for air, and cameras don't have exterior volume set.

[FarbigeWelt]

You by mistake set the air ior to absorption slot, so it was at 1.5 for air, and cameras don't have exterior volume set.

Wow! Thank you lot, what a crazy mistake. In this case I have to repeat the renders I posted lately. However, I wonder about the difference between openCL and BiDir and so on because it is the original file of first linked post. Well, it needs clarification that is clear now.