There is obviously more on the page and script because with both applets not having the initial update enabled I am wondering how you can click on a bar in the chart when is should not run the underlying query or display anything?
Perhaps consider isolating just the first applet on a test page to alert the event to make sure it is really only firing once per click in the bar. You can also add the Trace PARAM in your applet tags with a value of true, then observe the information in the browser java console.