I did an auto-save to generate the login. It had the username, password and all three submit buttons.
When trying to auto-fill it filled correctly but then submitted using the "Apply Now" button rather than "Login". I would expect it to use the button closest to the credential fields. In this case they are both inside the same table while the other two buttons are elsewhere.
Slightly more bizarrely, I tried to turn off auto-submit to allow me to login with the correct button by setting the login's Submit option to "Never". It completely ignored this and submitted anyway. If I remove the extra two buttons from the login item then it works correctly.