It seems that if one starts a community, then logs in as that community and adds people to that community's friends list, then all those "friends" are listed as members of the community...whether or not they have joined.
This may not seem like anything more than a slight annoyance since you don't actually get community spam unless you add the community to your friends list, but in some cases, I think it's more of a privacy issue.
For example, the community, "medicational" has many people added to its friends list. Some of these people may not want it to be so obvious that they're taking medication. I know in the eating disorders community, some of the people have started second, secret journals, so they can participate without their friends and family knowing they have an ED, so I'd assume it's sometimes likewise with medicational or other journal communities.
Perhaps, there is a way to sew this little loophole up, so that people can maintain a little bit more control over what is attached to their journal.
Just some thoughts. :-)