Paradigm reservoir bubbles?

while I do get bubbles...i've managed to get them out too.
i was wondering if anyone here also has a problem with the plunger portion of the reservoir?
it will sometimes NOT unscrew from the reservoir.

I often have problems unscrewing the plunger without letting in massive air bubbles. Solution: loosen the plunger before starting to fill the reservoir.

Almost every time I change the set. Not sure where it comes from -- I can't find any moisture where it shouldn't be or any other signs of leaks.