Update the ExpandMode property to allow zero, one or zero, one ,and multiple expanded items.

Implement IsExpandOnDblClickEnabled logic

ExpandAll/Collapse issues, Child RadPanelbarItem is resized incorecctly

PanelBarItem with no Items is initially expanded when its IsExpanded property is data bound

If the RadPanelBar Orientation is Horizontal, a RadHtmlPlaceHolder cannot be displayed inside a RadPanelBarItem

The IsTabStop is set to false in all RadPanelBarItems and set to true in the textboxes in the Items of the PanelBarItems. When tab navigating the RadPanelBarItems get focused, in Silverlight they don`t.

When the RadPanelBar is oriented Horizontally , The ScrollViewer does not work when the mouse wheel button is used.

Exception is thrown in the designer when threre are many items in the PanelBar control.

When using the new DragDrop logic in the RadPanelBar control, the MouaseOver state of a dragged item isn't cleared on drop. This is why as soon as you move the mouse over another item and start dragging it, you get two PanelBarItems in MouseOver state in the PanelBar.

When an level 2 RadPanelBarItem is selected initially it is stretched. Pressing the Enter key will resize it so that its children fit. 

As a workaround you can subscribe for the PreviewKeyDown of RadPanelBar and handle the event if the item should not be collapsed.

private void OnPreviewKeyDown(object sender, KeyEventArgs e)
{
    var panelBarItem = sender as RadPanelBarItem;
    if (panelBarItem != null && panelBarItem.Level == 2 && e.Key == Key.Enter)
    {
        e.Handled = true;
    }
}