Strange. Mine's never done that. Other than that, does it appear to be healthy? Does it spend most of its time out of its tube? What/how do you feed it? Have you changed it's diet lately?
I'm not sure how those types of worms spawn. Back in August, I had some tiny red feather-duster-type worms on one rock in my tank. A while later, I had white specks everywhere. After a month or so, those tiny specks have grown and I now have tiny red worms growing all over my other rocks and shells. I don't know how they spread, but it's pretty cool!
If your coco worm is actually spawning, you're very lucky! I haven't been able to find any good info on how that happens. If it was me, I'd probably leave a couple of the capsules in the tank just to see what happens. (Monitor your ammonia level, just in case). Maybe they'll just decay or disolve, but maybe you'll be lucky!