Thread:Project:Support desk/Username lowercase/reply (3)

Sorry, I don't know either, but page titles actually really seem to be the main thing to look at: Also when a user is created, it is not only checked, if the username matches the conventions, but also, if the page can be created (which e.g. disallows usernames containing things like "../" as browsers would then no longer be able to open the user page).

If you are interested in that topic, you can read the sourcecode in includes/Titles.php. Maybe it contains a comment on why the first letter is uppercased.