Isn't the confusing just coming from self-declared flight rules when flying without FPL?
I once learned that flight rules have to be declared before takeoff and are either VFR (V) or IFR (I, Y, Z). There is no such flight as partVFR-partIFR.
If instruction takes place, FI is PIC and logging IFR seems perfectly fine. Yes, I heard the trickypicky rumor that FI log more student flights as IFR then they are conducted, but as long as we allow IFR@G w/o FPL I see no other way as pledge to intelligence.