As far as I know: a symbol is quite the same thing as a MovieClip in Flash's Actionscript. Since they have own timelines, objects converted into such encapsulated things lose their appearance context you set on the main timeline (as it was in AS3 MovieClip(root)) for them. I think, you need to re-set the relative dimensions of your symbol in context to your main timeline (Stage). Then you need to set the dimensions of each of your objects within the symbol relative to the symbol.
Maybe one could get closer, when you post a screenshot or your project url to look into your code...
Hey salesdigital, thanks for posting your solution! Beat me to it We understand there's a few pain points when using scalable layouts and we're looking to make this process easier in the future.