Quite possible it is cross contamination... Blue can be very persistent.
As long as the blue isnt more aggressive than the PC you should be fine. I am not sure how to properly address that, since if you just rub it, you will likely spread the blue. If you try to kill the blue, you would likely also kill the PC.
I think the PC is normally more aggressive than blue and should contain the contamination but it bears keeping an eye on. I have had cams in my cave, in their own container, and havent had problems with cross contamination, other than a couple of very small spots that soon disappeared. With my blues, I tend to get a PC type growth on them after the blue begins to die off, but then I think that is kinda normal.
Perhaps someone else has a good answer?