Uhm, I have no clue where to start, but something really weird has happened in the last few hours.
If you click my profile here, you'll see a 5k rep user on Stack Overflow:
http://stackoverflow.com/users/1329111/sherlock
However, if I log in on Stack Overflow with the same credentials I used moments ago to log in here, I end up with this user:
http://stackoverflow.com/users/4713737/user4713737
I searched, but didn't find any issues that could help me. I'm lost.
I tried to get on Super User (for the first time)
Your original account has a Super User profile associated with it that's about 2 years old. Are you sure you've never been on Super User before? :)
It's unfortunately difficult to reconstruct exactly what happened here. It sounds like our global authentication is at play + some form of error on login. I don't see any exceptions in our logs, so that trail kind of dies there.
I merged your two accounts, so you should be back to one (your original) with the same Stack Exchange credential you've been using.
We'll also look into improving the "My logins" part of the profile to make it more clear what editing it will do.
Sorry 'bout the inconvenience and the confusion.
After Anna's answer I can reconstruct what happend. I'll just post it as an answer for future reference. (I tried as a comment, but it was kind of hard to read.)
What I should have done, is just delete the unused SuperUser profile and log back in to create a new one profile with the correct profile settings (the same as I'm using on Stack Overflow now).