When doing clay renders, if I have an object with material assigned to a polygon selection in the final render the result is a grey material in the place of the main material of the object. In the attached image you see for example walls, floor and ceiling are a unic object with polygon selection for the floor, and a material is assigned to it. in the render, corona doesn’t take in account the main material object and it renders in grey. Did you noticed something similar?
Hi marcotag! I was fixing a similar issue lately and I thought all cases were already covered. I’ll try to reproduce what you are describing and fix it. Thanks for the report!
Ah nice! I thought I was the only one and I didn’t report it.
Basically whenever you use a selection tag then that selected part won’t be affected by the Corona material override.
Definitely thumbs up for reporting this! 
Hi Houska, even in very simple scene it happens! see here attached
Thx
Studio object infinite.c4d (243 KB)
I can reproduce the problem with your scene. Hopefully Houska can too