So I'm thinking there should be a paragraph, added to the end of the Minsec/personal section, on the order of:
Setting the minimum security level of your journal will not affect the interface for making a new journal entry, whether you use the Update Journal page or a downloaded client. The interface will still appear to default to "public", regardless of your minimum security setting. However, when you submit the entry, LiveJournal will automatically change the security of the entry as necessary, so that a lower security setting is automatically changed to the minimum security setting before the journal is stored. (If you have the minimum security level set to Friends-Only, then any Public entry will be converted to Friends-Only when you submit it; Private entries, or entries that use custom friends groups, will remain unchanged.) The minimum security setting only applies when you are first writing an entry, not when you are editing one.
...or, er, something. That's mildly bleh, but I think you all get the idea.
(And there could then be a line thrown into the Minsec/community thing about "As with personal journals, the minimum security setting does not affect the interface for making a new journal entry blah blah blah".)