Of course, this isn't just a Scottish problem. Years ago we used to own a transport cafe in the Manchester area, and I remember one trucker coming in and asking for a bacon teacake. Then double checking what he'd get, as he'd asked for the same up in Leeds, insisted that that was what he wanted, then then been given bacon in a currant teacake - and then the staff had all watched him eat it as they thought it was an odd combination!
Where we were, drivers used muffin, roll and teacake interchangeably.