Manual focus is a problem

Hi.
Has anyone else come across the problem in that that when the "in focus" indicator lights up in the viewfinder, is not actually the best focus ?
I seem to be able to focus better without it using with an old 50mm lens.
I just discovered the setting and thought "aha! that will help", but it seems worse than my own focusing effort.

Trust your eyes! Or at least trust them if the dioptre adjustment on the viewfinder has been set correctly....