RH F1: If the left foot as you say is lifted first, and "then he steps off" with the pivot foot, then I'll assume the left foot replants prior too the Rf coming off? Or this guys Hudini on helium.
What I'm picturing by the description, there's one of two things going on.
Either, F1 is moving the FF first with out simultaneously, in a smooth and continous motion, moving everything else? That sounds like a balk.
Or, the wrong read on first motion by F1. If the coaches and runners are focusing on the front foot only and intently, the near simutaneous movement of the PF might appear to be coming second. Definite HTBT.
But, FF moves first and by itself, better be going somewhere, except first.