The need to change a Slidebank password every time usually means the user is logging in using browser-saved login credentials that are out-of-date.
To fix this, please go to the Slidebank login screen and request a fresh password using the ‘Forgot your password’ link. When the password email arrives, click the link to login with a new password, then you should be automatically prompted to save the new password by your browser.
Please note that clicking the new 'change-your-password' link might load a different browser from the one you normally use, so you might need to repeat this for each browser of your choice.
Only store passwords in a browser if you are aware of the risks involved in doing so, for example on a shared computer.