I don't know if this is something that happens to me only but when I type my password quickly in the login screen, terminal or any other panel asking to input my password, it throughs an error saying the password is incorrect. If I type it slowly then it doesn't give that problem.
I'm pretty sure it's not me typing the password incorrectly because I have been using the same password in win7 and I don't get any error even if I type it quickly.
I've noticed this problem even when using ubuntu on a different computer on a virtual machine.
My passwords contains upper/lower case and numbers.