"Malpractice" seems like a loaded word chosen more for debate impact than suitability. We can certainly agree that the original design was wrong (or "mistaken" if you want to load it on the other side). Isn't that enough?
I honestly don't know. I am hard put to explain what malpractice might be for a lawyer or doctor that wouldn't be the same for the largest US manufacturer of aircraft and her engineers.
This was a huge mistake, and it seemed as though they should've known.