Actually, you see this message if and only if you have 10 or more messages no matter what archive/unarchive state they are in. Just having an archived message isn't enough to trigger this message.

I like the behavior that jcwren describes better. Though I'd rather have Plus 1+5 messages displayed: shorter text and with the count of archived messages separated from the count of unarchived messages that aren't being displayed because you have more than 10 of them.

        - tye (but my friends call me "Tye")