Hi Cuong
In principle what he's doing is right, if there is no content in any of the other panes. Maybe I'm wrong but I concluded that the content from the other panes shows up in the contentpane. If there is only one pane that should be the reason for his problem IMO, if I understand what Whitt wrote correctly.
Another aproach could be to use the print functionality of DNN, just check the link that the print icon generates, it will show only the content of a module, but the problem here is that you would have to pass the module id in the query string.
IMO