I hate to be the bearer of bad news, but I'm another user that has experienced massive problems with the latest Safari plugin and 1Password. Fortunately, I still have the old Firefox,...otherwise I might just have switched programs.
Anyhow, the latest problem occurs when you have the latest Safari Extension (3.8.5) and the latest 1Password for Mac (3.8.7 build 31168), there are problems switching between 1Password accounts. I have two accounts--1 for work and one for home. Before, and with the old Firefox plugin, they work fine. You can switch between them and the browser updates accordingly.
Now, however, when you try to switch, the Browser does not update. At first you have to use the old password. Then, it seems to merge both accounts!!! So when I go to look through it in the Safari browser or the actual program, I found passwords from both accounts stuffed into one. THIS IS HORRIBLE!! I am very thankful that my personal passwords were not exposed at work!!!
I confirmed this several times. I separated the passwords into two files. Then tried to switch between the two files (going to the preferences in 1Password for Mac, and choosing another key), and then trying to use it in the Safari Browser. I still have to login with the password of the first key and then... I find both keys merged together into the second key. (almost as if it just synced the two together instead of loading the second key).
This really needs to be fixed ASAP before another version is released because it can easily compromise people's passwords. And in the future, please don't release plugins that aren't fully tested. This seems to be a fairly obvious problem. And from the other user forums, it appears many other folks have had issues with these beta plugins as well.