If an online Java application starts behaving unusually, it can be a good idea to clear the cache of temporary files that Java stores (you may want to do this in conjunction with clearing your browser's temporary files).
Click on the Start button and access the Control Panel.
From the list of available options, click on Java.
In the section labeled "Temporary Internet Files" click on Settings...
Near the bottom of the window that appears, click on Delete Files...
Ensure that Trace and Log Files and Cached Application and Applets are checked, and then click OK.
When the window disappears, the cache has been cleared.