You have to be logged out for this bug to occur.
First download any map in the database section of the site and completely download it.
Second, try to log in. When you click on the "log in" button, it acts as the download link again. When you cancel, and click on "log in" again, it will give you a critical error explaining that you have already have logged in.
This is an annoying bug on the site that I hope the administrators will fix.
Oh and please delete my new topic post in "Technology & Computers" because I posted this exact topic there without noticing this one partially dedicated to bugs. heh... (Please don't hurt me X_X...)
None.