Question on oxidation of brass inserts in shafts

So I have this Jacoby ultra pro in 5/16x18 using a brass insert. Been using it over a year with no issues. The pool hall in my area just opened today after 3 months, and when I took out my cue from the locker, a blueish green powdery substance could be seen in the thread of the male joint protector, which I believe is the brass oxidizing.

So my question is, is this bad?
Did 3 months of inactivity cause it to oxidize? Could it possibly have something to do with the manufacturing, or was it my own neglect. And if it's bad, how can I fix it?

Thanks in advance for any help you guys could give me.

Thanks for the help, so I'm guessing for humid areas, a shaft with wood or phenolic threads would be more ideal?