That reaction is mold or fungi in the bud. That isn't to say it's bad or stale but it just has some. Why and how could be a LOT of things.
I noticed similar changes moving from growers I knew to the stores and then to my own stuff. #1 reason to do your own is keeping it as healthy as possible.
Yup, certain strains block me up and others don't. I think that there has to be some mold or somethin in the bud even if its a small amount or its just allergies.. but i'd bet on mold.