Validation issue

I’m using this validator but it’s not fully working. I’m using it to check for an existing username. If I enter one that exists, the form doesn’t submit (correct) but there is no message displayed. If I change the username to one that doesn’t exist, it inserts the record but shows the message ‘that username already exists’. Is this a bug? I’m running v2.0.0 (I’m updating every time a new version comes out).