Email address and password incorrectly autocompletes in form

We have built a web site which requires a login (email and password). Safari autocompletes the username and password and that's fine.

However, within the system is a screen which enables the management of users of the system.

Despite the form and the input boxes both having autocomplete=off Safari overwrites the email address and password fields with those of the logged in user (even though they're already completed)!

I can understand why; I can't figure out how to stop it filling every username and password field it finds with login data.