If you want to have more than one FeedbackPanel on a page, but don't want to show errors messages in both at the same time use the following to filter the messages.

FeedbackPanel feedbackPanel = new FeedbackPanel("feedback");
feedbackPanel.setFilter(new ContainerFeedbackMessageFilter(YourForm.this));
add(feedbackPanel);

Now only error messages reported by (direct or indirect) children of YourForm.this will be shown in the FeedbackPanel.