That's what it looks like, which of course is an MS thing. When I did my tests I did as 'save-as' to get rid of that extra mirror data. Plus that setting seems a bit flaky because on some files, I had to do a save-as to see any difference at all.
From what I can see, the assembly respects the individual part settings. If the setting is unchecked for a particular part, SolidWorks will not save the tessellation for that part when saving from the assembly.
Another big deal about all of this is how much faster the files save! It would be nice to see some results on the time saved.
I would suggest that you modify your part templates to have that setting disabled so that any new part you make will be ready to go.
Mike Wilson