They have two separate fields - first name and last name. You fill full name in both
@mzel: Sorry for the trouble! I added something to my cart and then went to guest checkout to test this, and it filled my first and last name correctly. Can you tell me what OS, 1Password, browser, and extension versions you're using? Maybe there's a difference in our setups that I can test to try to reproduce the issue you're having.
Win 7 SP1 . FF 38.0.1
@mzel - I tried this both as a guest and when signed in and I also could not reproduce a problem. Could you send a screen shot showing the fill problem - maybe we are looking at different pages?
Please tell us which version of 1Password you're using along with the 1Password extension. The filling is dependent on the 1Password versions and it could explain why we're seeing two separate behaviors.
I've also moved your thread to our new dedicated forum just for saving and filling issues in web browsers.