Racket Distortion after Stringing

When I mentioned to some folks about how two of my ProStaff Classics (RA72 stiffness) distorted after stringing, few believed me. They thought it was impossible and that I was crazy and just being picky! It was a pity I did not take pics then. 

One racket lengthened by 9mm and the sweetspot totally disappeared. When I brought it back, the stringer simply dismissed it as "manufacturing tolerances". That was one of the first few brushes that drove me to buy my own stringing machine.

History keeps repeating. Names withheld, two matched ProKennex Black Ace 98s suffered the same fate as my ProStaff Classic.

The chap (named DL) met up with me and asked why was one of his racket totally unplayable.

Let the pics below speak...

The top racket had yellow mains, bottom one had blue mains. 

Both DL and myself tested the rackets. The hoop length of the racket with blue mains was compressed 12mm shorter. Take a look at the last pic above, near the words "Precision".

That's why I usually measure and check the hoop length and width before and after stringing (link1)(link2). If the difference exceeds 5mm, I usually cut and re-do everything from scratch.