It's not a design flaw. The rear input is intended for use with, i.e., a wireless receiver. There was no scenario where someone would plug directly from their guitar into the back of the unit so the Auto-Z circuitry was not duplicated on the rear input.To be honest this looks like a design flaw to me. I can't think of any reason why the two inputs should be treated differently.
What is wrong with everyone lately? So much negativity and accusatory rhetoric.