Well, one possible guess is that the new growth could be making the roots look thicker and the ends appear thinner. Or, maybe you've had some breakage along the way and a nice trim would help things get back in order. Did you see the latest pictures of Supergirl's or read her thread on her issue with thin ends?
I dealt with my thin ends by getting a nice trim. It was worth it! I don't have to do anything to "mask" them b/c it never worked anyway. HTH