I use 1Password on both Windows and Mac, primarily with Firefox. This issue appears to be present on both platforms, but I figured I'd start here before crossposting to the mac forum.
The issue is that I have more than one google account. For almost all websites where I have more than one set of login information, hitting the shortcut hotkey will bring up a prompt for me to choose which set of account information I want to use. In cases where the username is already filled in (i.e. I'm already logged in but it wants to verify my identity before I make a purchase), 1password almost always selects the right password based on the username which is present.
Except on Google. If I'm logging into google, it always assumes that I want to use one account or the other, rather than giving me the option to choose. When it's verifying my login (i.e. username is already filled out) 1Password always gets it wrong and puts in the password for my other account.
It's not a major issue, but it is annoying, because I use my google accounts a lot and this crops up every time I want to switch, or buy anything.