ITA. MNT are heavy protein based products. Keep in mind that it also can be used on animal hair (coats and hides)--so it does carry a certain extra level of ingredient potency because the animal hair can probably take it better than our little hair fibers.
Samaria, you using it as a leave in is probably what caused you the tangly breakage. I also use MNT, but only when my hair is terribly protein deficient. I never use the conditioner as a leave in because it is much too potent for my hair-- even when I'm rinsing it out. Many times, I don't even use the shampoo/conditioner combo together at all. They are much too protein rich. For the protein to cause that sort of issue for you, you were probably already properly balanced protein wise or very close to it. The addition of the extra protein aggravated the protein balance resulting in rigid, tangly, over-structurized hair. If you would have done the same thing at a time in your regimen where you were protein deficient, I can almost guarantee that this would have been an MNT praise thread
The only solution to this is allowing the protein to wear off (which it will in a few washings and deep conditionings) and really infusing your hair with moisture at every turn. That means cutting back on protein in other products and areas in your regimen (moisturizers, leave ins, conditioners, etc). HTH.
For the girl who had to cut her hair, I'm also leaning toward the bad batch hypothesis. That, or the stylist didn't recognize the protein overload and instead of really working with the hair, decided to take the easiest route and cut it off.