The new logout with checkbox thingy is broken.
Thank you for logging me out on stackexchange.com and stackoverflow.com, like you are supposed to. And also (very helpfully) logging me out of askubuntu.com, mathoverflow.com, serverfault.com, stackapps.com, and superuser.com as well.
Unfortunately, I'm pretty sure I don't have accounts on all those sites. I only have accounts on stackexchange.com and stackoverflow.com.
This is broken on Chrome 45, but works correctly on IE 11.
This is what it looks like on IE 11: