Reported in issue 13143:
Opening the F8 menu prevents vncviewer from terminating when it loses the Xvnc connection. Not surprising as the menu opens its own main loop. We've had similar issues in tlclient.
Tested with client build 2284 on Fedora 33 and server build 2266 on Ubuntu 20.04, and this issue is still present.
1. Log in to the session.
2. Log out. When the window with "You will be logged out in 60 seconds" show up, leave it alone.
3. Press F8 to open the menu.
4. Wait for the log out to happen.
5. The session does the log out animation, but the client window is still open. If you press F8 or the list items in the menu, the window will close.