Perfectly normal. They are just worms with cool tails. He'll find a new place he likes and set up shop to grow a new tube. Only thing to be concerned about is that your calcium levels are up over 300 so there is plenty available for him to work from.

We've got one that his whole tube is now covered in green star polyps, it looks really odd, like he needs a shave or something. I'd guess he may off and move it becomes too crowded leaving a peculiar looking patch of GSP's. If so we'll end up with an interesting frag anyhows.