On a site we're currently working on, clicking Logout in the CMS (or going directly to /Security/logout) doesn't logout but instead just takes you to the CMS.
No core files have been changed, and it is happening in 2.2.3 and 2.3.0-rc2.
It's also not happening on another site operating off the exact same core 2.3.0-rc2 codebase (symlinked).