Graphite necks will move, and anyone who says that they don't or can't is flat-out wrong. I had a Modulus Q5 a few years ago...one of the older ones without a truss rod. After changing strings from an unknown brand to DR HiBeams, the bass developed a pretty bad backbow and was unplayable. I called Modulus, thinking that I would need a new neck. I described the problem to their tech over the phone, and he replied by asking me if I was using DR's. When I said yes, he told me to throw another brand on the bass and assured me that the problem would go away. I thought he was either lying or crazy, but I did what he suggested and put a set of GHS Bass Boomers on the bass. Within 2 weeks the bass was back in perfect relief. I have since learned that DR HiBeams, which are great strings IMHO, have a much lower tension than most other roundwounds of a comparable gauge.
Bottom line: graphite necks move.