I can't way in on the legal issue, since my tint is at the legal limit...
But I have had my tint on for nearly 10 years. The back window is badly bubbled but the sides have no bubbling. I use my defroster almost daily in the winter. Don't know if that is the cause or if it is just coincidence.
Defending the reputation of the red-headed step-child of the focus world for far too long.