News you said
"To answer the question. They were taught that way. And taught a bad habit from someone who was wrong".
I think you are quite possibly correct.
A call I have heard at several QLD regional airports over the last year or so is;
"ABC taxying for the training area, ONE PLUS ONE."
I guess they are saying this so that ATC understands that there is an Instructer on board, but where does this appear in the AIP. Seems that some Flying Schools are making up their own radio calls and teaching this ability right from the beginning.
BTW what is the radio call when the Instructor is not on board,....ONE MINUS ONE!