Google likes to make it easy for us to use Blogger and Google. When we login to GMail, and we have a Blogger account based on that GMail address, our Blogger access is provided, with the GMail login. It's not provided seamlessly, but we don't have to repeatedly login with our GMail account name and password, for each different Google application. That's a convenience - of a sort.
Unfortunately, what's a convenience to us may not be so to everybody.
When a user submits a comment, I get the email, click the "Publish" link, and...get kicked off Blogger and GMail (i.e. my Google Account session is killed).
This may have something to do with the fact that my GMail and Blogger accounts are rather old, and different from one another (my Blogger username is my email, and my GMail username is the username component of my email address).
When we log in to Blogger, or Google, a cookie is created, and the cookie is used in all subsequent sessions in various authenticated Google processes. Blogger, Docs, GMail, Picasa, and many others share one cookie. And that one cookie contains but one identity.
If you use simply one single browser for Blogger and GMail, and a different account for each, you'll be constantly logging in again, each time you refresh a Blogger or GMail display. This will also affect cookies which need to be persistent across browser and login sessions, as is currently a problem with Blogger Stats and the "Don't track my own pageviews" setting.
If you want to use multiple identities, then use multiple browsers, or multiple computers. Or use a sandbox, to use the same browser, in multiple copies, on one computer.