Try typing in something different into the password box and when it asks if you want to save it, say yes. It will then say that you have entered the wrong password. Type the correct one in and then say, no, you do not wish to save it.
You will need to disable the AutoComplete settings in your browser. In IE click Tools menu > Internet Options > Content tab > Under Personal Information > AutoComplete. Uncheck the box for User Names and Passwords on forms and click OK etc.