It has to do with account migration. When you login with your google accounts login and then enter Blogger.com,
- It enters www.blogger.com/start and then
- goes back to the Google Accounts page (which hosts the Google embeddable login box), which returns a true (or whatever indicating successful login) and then
- goes to www2.blogger.com/start (since I have migrated to the new blogger account) which
- returns back to www.blogger.com/start (assuming that the user hasn't migrated - or whatever) and this continues.
This page flow is actually a valid test case if you have not migrated your account (I guess).