I've had a similar problem before where the turbo-prop I flew rotated about 10 knots before Vr on the take-off roll. It turned out, since the flight was not full, that passengers took their own liberty to change from their allotted seats to sit closer to the exit at the back of the aircraft.
Maybe flight attendants should have a basic understanding of aircraft weight and balance so they can at least recognize a balance issue if the passengers moved seats before departure?