Using google chrome, pressing tab or return to submit login information sends the focus to another form input rather than submitting the form. This may well be a problem with all webkit-based browsers.
Correction: tabbing to the submit button does work correctly.
I'm unable to tab to the submit button. Using webkit-SVN-r41760 for the Mac. The tab order is User Name > Password > Address Bar. Hitting return in the password field reloads the page instead of logging in.
I was also able to reproduce using midori, a webkit based browser.
Fixed in cumin 3184. The login form (and any other form that has an input box) should submit when the Enter key is pressed.