Hello,
I notice weird behavior of lights, artifacts (much more noise) as well, I haven't had time to check everything properly and test it via 1.5 but now that I see this posted around, I guess my eyes weren't deceiving me. I will post shortly very similar issues, I'm in the middle of a tight project at the moment.
I've noticed that putting a portal light, gives me exactly those kind of artifacts (show in the image posted by Marchwiany) in the ceiling, (direct light) while darker areas area clearer than with NO portal light. (this happens on a square room with one wall being completely opened.