Java SE (Java Platform, Standard Edition)

I've already developed an application written in VAADIN (a java library to create web GUIs) to have a web maintenance interface for an application. Everything works fine and development was really fast, but now I'm trying to browse the web interface using the JavaFX WebView component and I'm suffering some problems. If I start reloading the URL after several tries the background of the buttons does not load. I tried changing the cache of the Jetty (used for browser VAADIN pages) to 0 without results.

Once it fails the following reloads don't solve the problem. I cannot reproduce this problem using firefox or chrome (who has the same engine as WebView I think). I also tried to reproduce the same situation using the demo "http://demo.vaadin.com/sampler#ButtonPush" but in this case the problem does not appear in the same way, even though the background of the button can took several seconds in some situations.

Any idea? Any relevant configuration in the webEngine?