branch_security=on
will this completely hide the branch from other members?
set the branch_security=on and workarea_security=on in iw.cfg file and all the branches that you have in teamSite set the permission to rwx-rwx-000.permission depends on your environment and 000 says No access, same thing for workarea.
i tried the branch/workareasecurity=on and didnt work for me.
I hope you are not using that syntax.What's in your iw.cfg?