clicking on 'tray' leads to 'Unsaved data' message

I have a tray on a Web dynpro ABAP screen. If it is clicked (without any other action taking place) and then the browser close button is clicked, we are prompted with an Internet Explorer 'You have unsaved data' message'. I've tried to use the 'l_portal_manager->set_application_dirty_flag' method but the message still appears.

Any ideas?

thanks,

Malcolm