Backend call in Window Closing handler?

How can I make a call to the backend in a Window Closing handler ?

What I want: automatic logout of the member when he closes his browser
window.

I tried both a FormPanel.submit() and RPC call, but neither do the
arrive at the backend (in dev mode) :(
They only arrive at the backend when I show a browser alert popup by
setting the message in the event that is received in the handler.
Example:
----
private final class CloseHandlerIntern implements ClosingHandler {
public void onWindowClosing(ClosingEvent event) {
event.setMessage("automatic logout");
createFormBuilder("123").submit(); // FormPanel.submit()
// getServiceFacade().logoutLoggedInMember(); // RPC call
}
---

Any idea how this can be done?
I am running GWT 2.3 in noserver dev mode.
I also tried the CloseHandler, but it gave the same result.
I notices some old open issues about this subject like 6088.

- Ed

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