Application is hanging in WebView

I am currentley implementing a special JavaFX Client for my application. Basically the FX application is doing nothing else then loading a vaadin application into a WebView. And this is alos the problem, and it seems that again and again the problem has something to do with the push mode, which the application is using. I write again and again, because in the last view years I had a lot of problems with the push mode of the atmosphere framework. I do not know if the reason is that we are using glassfish as application server, however sometimes it really made me angry.

The vaadin application is loaded without any error into the webview. But if I start working with the application (in this case pressing a button) the valo theme loading bar stops at the half and the application hangs.
Therefore I started the client with enabled firebug, and there I can see that a second get request is hanging, see the attachment.

However the application is working fine in any other browser. The WebView is using the Mozilla/5.0 (Macintosh; Intel Mac OS X) AppleWebKit/537.44 (KHTML, like Gecko) JavaFX/8.0 Safari/537.44 engine.

I hope someone can porbably tell me why I am facing again and again problems with the push mode.