Platform parsing takes the first part before a dash for family name, so "macos-sierra" and "mac-os-x-elcapitan" end up in different families.
Created attachment 305557 [details] proposed fix
Comment on attachment 305557 [details] proposed fix Clearing flags on attachment: 305557 Committed r214513: <http://trac.webkit.org/changeset/214513>
All reviewed patches have been landed. Closing bug.