I tried to set my status to invisible in Gmail Chat, but I got "Oops! You are not invisible because you're logged into Google Talk from another client, device, or location that doesn't support invisibility." message.
I used the "Sign out all other sessions" button, log out from Google+ Hangouts and use the old Gmail Chat. Then logged out and turned off all my devices (web browser and tablet), and checked with a friend if I was connected, and I still was. Also removed access to all sites, apps and services, even unlinked my account from the tablet. But the problem persists.
How to really disconnect from the Gmail Chat?