Safari (keychain) fills in the wrong password or email

I have this problem with Safari a lot. When I create a login to a website, and Safari asks me if I want to save the login, I click Yes. Then later, when I revisit the same site, Safari auto fills in the login info, but then the site says it is incorrect. VERY annoying!

The login box has only two pieces of info: my email address and my password. When I click on the disclose button on the password field, it does look like the type of password I create. So perhaps the email Safari filled in is wrong? Why does Safari do this?

Another problem is when I click Login or Continue, and the website returns the message that it is the wrong password/email combination, Safari sometimes asks me if I want to save the login! Why would Safari do this? Is Safari that stupid? Can Safari not read or detect that the website is returning an error? How long has Apple had to refine this feature?

Poor software like this is why many people find passwords to be such a pain and why bad passwords and bad security are such an issue to this day.