This really isn't a question specific to MyFaces. The primefaces forums might be a more appropriate place since you are dealing with primefaces components.
However, Have you set a breakpoint on setSubmit() to see what is calling it? My guess is that either actionStatisticsEventUserCategory has a scope that loses the changes, or that you have more than one object calling setSubmit(). You should also add some kind of messages component to the page to display any errors that might be generated.
