When logged into 1Password (so that hitting the autofill shortcut fills automatically, without needing to enter your 1Password password), hitting the shortcut -- CMD + \ by default -- and holding command for just a second too long will open the login tab in a new page, as if you had manually clicked the "Login" button while holding command.
1Password Version: 5.3
Extension Version: 4.4.2
OS Version: OS X 10.10.4
Sync Type: Dropbox
Referrer: forum-search:Holding command