Right now only one Item can be the currently selected item in a panel bar even if multiple are open. I suggest that we can set multiple selected items (more than one opened panel can have the selected class injected onto the header) 

One possible way this could be achieved is setting the selected attribute to True, and letting the developer deal with toggling the booleans on his end. (As of now, the panel bar will override the selected values as soon as one panel is selected)