fideliti.co.uk appears to have a fairly simple login dialog. When I fill the values from the browser extension (chrome) it fills them correctly and it looks like it tries to invoke the login. The page just reloads and clears the values.
If I copy the password into the form and trigger the login by hand it seems to work ok.
1Password Version: 6.2.1
Extension Version: 126.96.36.199
OS Version: OS X 10.11.4
Sync Type: (family default)