@pfefferle I think that's what used to happen, yes, but I can see how that wasn't ideal. Still, it was better than not being able to comment at all under the 'enable blog' mode. There are pros and cons to the 'enable authors' and 'enable blog' modes.
I suppose there's no simple way to have both a blog profile (for all posts) *and* separate user profiles (for comments only).
Thanks for looking into it!