As KayKayKay says, web forms are somewhat unpredictable. The can be implemented in many ways, and even on a computer they don't always work as expected; though I grant they do work more often. Mostly, I suspect, due to the fact that web developers have been dealing with and eliminating problems with the desktop browsers for much longer than they have for the more limited mobile versions.
on the shortcut issue, Imaaged to set up the shortcut I the settings function. I setit sothatwhenI type z m , the screen shows my email address- quite smart of me so I thought! Unfortunately when I do this when filling in a web form, the email address is inserted but when I then go to the next item - say for instance a password, the form then resets!