Server Connection lost while downloading chart

While downloading chart as PNG/JPEG/PDF/SVG, it shows Server Connection lost notification as per attached image. After saving chart it disappears. Is there any solution available for this?

Are you using Vaadin Charts? What version of Charts and Vaadin are you using?
Can you post a simple example where this can be reproduced?

Yes…I am using Vaadin charts add-on having version 4.0.0. You can take example from vaadin charts demo to reproduce the scenario. In this example add one line conf.setExporting(true); One more thing to be noticed over here is, this is happening in Firefox but not in Opera,IE & Chrome. Thanks!