I figured this one out finally. It turns out that the data in the wp_usermeta table for user_id=1 (admin) was corrupted. This was apparently causing the SSL redirect issue when trying to login to any domains.
Once I restored the proper data for user_id=1 into wp_usermeta, everything worked fine. I would much rather have WordPress give an error like “hey, your usermeta data is messed up”, rather than have some strange random behavior like that.
Thanks for the help,
Dave