The 1Password main app has very recently begun stealing focus if it is open (but locked) when you unlock in the browser.
This causes the browser mini-vault thing to unlock as expected, and immediately get a face full of app. Particularly annoying if you have multiple logins which match the domain because it causes the mini vault to close, so you have to reopen it to login.
This was happening consistently until I tried to artificially replicate it while writing this ticket and now I can't get it to happen at all, but it was, I promise.
1Password Version: 1Password 6 Version 6.5.3 (653000) AgileBits Store
Extension Version: 18.104.22.168 (Chrome 55.0.2883.95 (64-bit))
OS Version: 10.12.2 (16C67)
Sync Type: Not Provided