I am planning to do an internship in a theoretical physics area for a year before applying for PhD. My current masters' thesis advisor (who is a hardcore experimentalist) warned me that I might not actually learn anything new in a theoretical intern, and that I will only end up solving some textbook problems. I was wondering how plausible this is, and if it is a strong possibility, how I can make sure that there is a significant addition to my skillset during my intern in theory. Anyone?
EDIT : This internship will NOT be a part of my M.Sc. I will be doing it to bolster my otherwise ordinary profile. I basically want to publish something or at least get a good recommendation letter before I apply for PhD.