OptionGroup valueChange event sends two requests from browser to server

I have a OptionGroup component in my VAADIN application with multiSelect set to true. I have a valueChangeListener registered on the component. When user click on the checkbox of the OptionGroup, two value change events are send from browser to server (analysed from Chrome’s Network tab). The first one, sends the index of items selected before the click and the second one, sends the index of all items selected after the click. Is there a way to avoid sending two requests? I need only the one after the click.

Note: When I tried to debug using VAADIN debug tool, in the connections tab, for the content of first request was just a “Shared State” text. I would like to know what is happening behind the scenes here.