Yes, it happens sometimes. Are you absolutely certain that the top of your plant is perfectly healthy - not showing any signs of poor growth, or yellowing growth, and the trunk looks healthy all the way up? I ask this because many Cordylines got badly hit by last winter, and the reaction of a lot of them has been to throw out new growth either at the base or up the bottom of the stem. You don't need to do anything, just let it grow on, but if you notice the top's dying back or going soggy or anything, you may need to cut the mainstem back to the new growth.