Covers the stunt where the three braces appear to toss the flyer upward and she arches her back with her head dropping backward (Parachute). Remember that bracers are located at the second level. The arch in this case would not be illegal because the flyer is maintaining the contact.
They can arch their head backwards while braced and they are in an inversion. Since their hips are actually not rotating over their heads, it is not a flip. My concern is that if they cited 3.3.1, then they think that this skill is illegal. If it was something about releasing the arms, that might be a different story, although they would have to release both arms for it to be illegal.
My feeling is that even if they considered it to be some type of arch enough to possibly flip, all possible inversion rules would have been covered with the setup that they have. Pretty much the only thing they cannot do in a braced inversion is land in an inverted position, and they did not do that on these videos.