protecting blogs in multisite mode not working

just converted an existing site with membership and bp installed to multi-site and I'm trying to make a sub-blog protected, but I'm not managing. Main site restrictions still work fine.

i have membership activated on the root blog, activating it elsewhere doesn't work as it treats it as a new membership installation. the blog in question is created via the network admin area by me.

the blogs do appear under Buddypress > Blogs in levels. I tried only selecting the main blog in positive, or the other blogs in negative, no difference, even logged out users can see the blog (limited to a visitor level, which guests also are assigned to).

not sure if there's an issue with adding multisite after membership, or if I'm doing something wrong, as there's not much documentation about multisite with membership. good chance it could be my installation (if you remember, there's been a few issues due to my migrating forums etc.), but just don't know!