I've noticed this too, but I think it is your 'Browser' that's doing that.
I have different 'email' addresses that I use on various 'sites', so obviously the 'Browser'
doesn't know which one I am using, until I start to enter the 'user', & then given a choice!!
It THEN knows the 'stored' password, for the choice you make.
Mind you, this has nothing to do with 'Cookies', which are a different "Kettle-Of-Fish", and
have to do with 'remembering' (feeding back) your I.P. address to check if you have 'visited'
before, and so that SITE remembers settings/purchases/views etc, but NOT your password.