I have a different but slightly similar situation: I can push one or both balls out of the sack and into the mons pubis. [Definition: The pad of flesh covering front of pelvis which surrounds penis. Covered by hair near penis. Pron. monz pyoo bis.] Stated another way, I can squeeze the sack from the bottom up and push the balls out and around the base of the penis. If I let go, and I'm warm, they'll drop back down into the sack on their own. When I'm cold, they have to be pushed.

I've read that this isn't common but not especially rare.