Not sure if there is a minor (potentially frustrating) error on the VPN Client GUI?
With a fully functioning active VPN Client connection, attempt to manually stop the VPN Client:
Click the OFF slider, and the 'Applying settings' spins on screen for about 10-15 secs.......but the Service State slider remains ON in green in the GUI.
I can't reproduce it here with vpnbook's free server. My guess is your client is taking longer to shut down than what the webui waits for before reloading the page, so the page gets reloaded before the client has exited. can you see if that's the case by tailing /tmp/syslog.txt whole the page is reloading?