So I have a problem with newer browsers saving passwords. Say I have a password box like so:
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Have you tried changing the name attribute to something ridiculous? I believe the autocomplete functionality is based off the name attribute. I'm not 100% sure but in the limited testing I did changing the name attribute was changing what type of autocomplete data was being presented.
Obvious example just to be clear: name="username" was showing my username while name="email" was showing my previously entered email addresses. When I switched to name="browsersAreStupidForImplementingThisFeature" I didn't get any autocomplete data.
Needs further testing but might be a good place to start? Good luck