@dh024 It does the same as clicking enter (or checkmark) on the keyboard after filling in the password. Unlocking the vault from the dropdown menu in mobile website password fields.
However I do agree with the OP that the location of the button at the top is confusing as I have accidentally logged out with the large bar button underneath the password field.
Maybe the two buttons can be switched around?
I think Unlock serves as a useful label, so I would leave it where it is. If it has a secondary function as a hitting the Enter key, that’s doesn’t seem very critical. (Does anyone actually do that??)
So, the root of the problem is actually the button bar underneath that logs you out. Perhaps that needs to change - either provide a warning before logging out, or change it to a conspicuous button (like a big red X button).