Strange problem with login-screen

A few days ago a problem started to appear when changing realm. This is what is happening:

I open wow, type in my password, getting in queue to Lordaeron since I'm most active there. I see the huge queue and decide to play on Blackrock instead. When I press "Change Realm" the "queue-box" disappears and I'm back to login-screen... So I enter my password again but this time when I press "Login" it erases my password and nothing happens.
It's an easy fix, all I need to do is to restart wow, but it still bugs me.. I want to find out what it is. Anyone have the same problem?

Try to clear your WTF folder. Keep in mind it will reset addon settings if you are using any.