Clicking "Log Out" from the user icon menu bottom left of the page redirects to this page:
but doesn't actually log out of bitbucket... upon navigating to bitbucket.org I land right back in my account without needing to login.
Only clearing browser cache appears to effectively logout. This is a security issue when not accessing bitbucket from a personal machine.
This appears to be due to use of third party cookies in the logout process.
It is not uncommon to disable third party cookies in light of excessive tracking through advertising now.