First, using Safari 6.04, 1password extension Version 3.9.14.
Second, here's the site: https://www.dymoendicia.com/login
Whether allowing 1password to create the Login or creating it manually (using the +), the result is a Login that doesn't work at all. Fields are either filled in incorrectly (likes to enter the word "search" into the account field) or doesn't fill in the fields at all. Very, very strange behavior that I, personally, have never encountered before.
I haven't tried the latest Beta, but could do that if you desire. Didn't see anything in the change log that indicated using it would help, but...