I don't know if this is a fixable problem or something inherent in PBR, but I'm reporting it anyway (especially since I've not seen anyone else running and recording little tests like mine). (PBR is so new that it's impossible to know what's a bug and what's a feature.)
When I move closer to/farther from a PBR object (like a mirror), the reflection seems to respond backwards of what I expect. Meaning: move closer, reflection gets SMALLER. Move away, it gets larger. Or being right in front of the mirror I'm not there at all. I first found this in the Firestorm Beta viewer, but went over to the SL viewer and the issue is identical.
This short video says it MUCH better than I can describe: https://flic.kr/p/2pEMy4C