If you try to ping a host all the pings are done in background. If the ping job takes a little bit longer you run in a communication error message and you will be redirected to the OpenNMS login page. If you login again you want to go to the topology view, the ping dialog is still open and shows an OpenNMS login page. If you try to close the ping windows the communication problem error message appears again and you are redirected back to the OpenNMS login page. It is not possible to go back to the "Topology" cause it always shows the broken ping window.
Even if you try any other Vaadin component you will be redirected to the OpenNMS login page.
You can verify this issue by ping with a large number of messages which is a similar behavior if you try to ping a very slow or offline device. To be able using the Vaadin components, it is necessary to restart OpenNMS, otherwise you will be redirected occasionally to the login page.