It is not actually changing your password. It is just showing more “dots” than your password has characters. In older versions of Windows, if you had a 5 letter password, it would show 5 starts or dots. Since this allows someone to get closer to guessing your password because they know how long it is, they added a new feature to XP so that it just shows a bunch of dots every time. All subsequent versions of Windows also have this feature. That way, it doesn’t give a hint as to how long your password really is.