As part of our development, we have no come scross the same issue as Linus, but instead of a straight postback, we have an image which pops up an alert box asking the user if they want to delete the item from the data collection that makes up the panel items.
I tried to implement Kate's solution below which does capture the correct panel item etc, and allows the delete popup to appear, but it still doesn't prevent the panel from expanding or collapsing.
panelBar = $find(
"<%= FavouriteOrdersPanelBar.ClientID %>"
panelItem = panelBar.findItemByText(args.get_item().get_text());
Does anyone have any idea why this wouldn't work?