If you create a new file, it makes it as an unpacked design and does not give the option to have a packed design.
If you open a packed file, Schematics unpacks it and only works on the unpacked design. It cannot save the work back to the packed file. You end up with both a packed and unpacked set of files with the packed file being out of date.
If you have Windchill running, Schematics defaults to packed designs in Windchill. It opens the design from the packed file and saves it back to the packed file.
With Windchill running and open a packed file that is outside of Windchill, it creates the unpacked design but then never updates either it or the packed design because it saves any changes in Windchill.