So no one really knows the fundamental cause of the pitch up!
Being dual rated on the 75 and 76 I never allowed pitchup to develop (tail strike risk, never aerodynamic braking) but on a landing by an FO when I was new on type he did allow a marked pitchup to develop which I stopped. He, being much more experienced on type thought I was being overcautious, but since pitchup is specifically warned against in the Boeing FTM I sometimes wondered about the fundamental aerodynamic cause!
I always assumed it was aerodynamic but never heard a full explanation.