I tried uninstalling and reinstalling the plug-in, but that didn't fix the problem. Here is my version info:
Chrome Version 40.0.2214.93 m
1Password: Password Manager and Secure Wallet 18.104.22.168
This guide has a checklist for you to review to figure out where the issue might be: https://guides.agilebits.com/1password-windows-kb/4/en/topic/auto-save-not-offered-win
First thing is to check if the auto-save has been disabled; open the main 1Password application, unlock with your master password, and press the Preferences button. Go to the Auto-Save tab, is Auto-Save new Logins unchecked? If yes, check it and then try again, see if it works.
In the same tab, there's the option Disable Auto-Save when Vault is Locked. If it is checked, you can't auto-save while 1Password is locked.
I hope this helps.