I think part of what you may be seeing is that on web access MC typically asks for the authentication credentials, but there's a box you can check that says "remember my authentication credentials" or something to that effect. So If you ticked that box (or left it ticked, I can't recall the default) subsequent network accesses from the same computer will go through without any request for credentials.
To test if that's the issue try logging in from a computer you haven't used for this before and see if it asks for credentials (it should). You may be able to "reset" things by clearing your browser cache, but I haven't tested that solution.
If you can log in to the web interface with no credentials on a computer you've never used to access the web interface before, report back, as that would be odd.