Are you sure you are referring the GSX vehicles used *IN GSX* and not, for example, Airport Services vehicles ?
They are also used as ground vehicle replacements so, they look exactly the same as GSX, because the are the same but, until after you select GSX and start something, they'll be placed according to the Airport service files, exactly as they would be if they were still default.
When you start GSX, all of these will be automatically removed, to be replaced by the "same" versions, now under GSX control, so they will start according to the start positions you saved.