If you are using the Mac App Store version of 1Password, please be sure to install:
1Password used to automatically submit forms using two different methods. One was good; the other one was less-than-stellar. The second method caused problems for lots of users. It would sometimes submit search forms instead of the login form. It would drink your last beer. It would make a mess and not clean up after itself.
The website version of 1Password used both methods to submit forms (depending on the situation), but the Mac App Store version only ever used the less-than-stellar method due to Mac App Store guidelines.
If Mac App Store users were experiencing specific auto-submit problems, we would recommend installing the script above which would enable the good method. It wasn't as much of an issue, though, because the less-than-stellar method was there, and even though it was less-than-stellar, it was something.
On May 27, 2014, we released the 4.2 update to the 1Password extension. (Note that this was only an update to the browser extension, not to the 1Password app.) In 4.2, we decided to solve a bunch of users' problems by taking away the less-than-stellar method from both versions. This left the website version with just the good method, but unfortunately it left the Mac App Store version with nothing. That's why it's now necessary to install the script that was only optional before.
We apologize for not making this information clearer and easier to find. If we can be of further assistance, please let us know. We are always here to help!