Hi Bruce, bracketing is conducive with processing your own film and printing. I know that labs often use automatic print density settings for the roll of film.
Not so sure if this is also performed for each individual frame printed. However if it were, this could certainly reduce the differences apparant with bracketing (the tone separation and colour shifts may be less apparant without changes in density also).
It might be worth asking the lab to print 'straight' without any exposure compensation adjustments between individual frames, to see if that makes any difference. They should be able to do this imo.