I have this problem with the Chrome extension as well as the Firefox extension. Hard to nail down exactly but it just seems to re-lock almost-but-not-quite immediately. Switching tabs makes it log again more? Also, the icon in the toolbar doesn't update properly so it looks locked even when it isn't, so you don't always know when the change happened.
1Password extension version 2.27.1 (Chrome at the moment)
Orion .99.128.2.1-beta (WebKit 619.1.11.111.2)