Nope, I use this usually when testing (my simple one-way mind doesn't support more than one pw for testing). This is how it works.
admin pw: 1234
Test_User pw: 1234
if you log in with [] (blank username) [1234] you'll log in as admin.
if you log in with [Test_User] [1234] you'll log in as Test_User.
if you log in with [Yo mama] [1234] you'll log in as admin.
Yeah, not quite safe, but hey, who's gonna have the same pass as you and mistype the username?