It's such a pain. I've had all kinds of oddities when using type="password" for private data. A lot of password managers would see that and assume a password and fill in the email in whatever the form element before it was. You can't tell them not to, either!

I've also had to scrub data when users somehow put their credit card numbers into public fields. Still no explanation on that one, but it happened with enough users that our only guess was browser auto-fill gone awry and people blindly hitting submit.