Placing the RadGridView control inside a PanelBarItem element does not display all of its rows when the GroupRenderMode is Flat.

A workaround for this is to place the RadGridView element inside a Grid layout and create a new RowDefinition with Height="Auto". 

<telerik:RadPanelBarItem>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <telerik:RadGridView/>
    </Grid>
</telerik:RadPanelBarItem>

Setting a RadGridView element instance as content for a RadPanelBarItem, causes the RadGridView to not show all of its columns.

As a workaround to this, you could set the IsScrollViewerInsideItemsEnabled property of the RadPanelBar element, to True, and you could control the expanded length of the PanelBarItem which holds the RadGridView instance. This could be done by utilizing the ExpandedLength property.

When a control is nested in a RadPanelItem, it is wrapped in another RadPanelBarItem. The DataContext of the second level item is not inherited correctly. As a workaround, you can bind directly to the element which holds the DataContext with an ElementName binding. 

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;
    }
}

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.

PanelBar: A custom template can not be set to a PanelBarItem, using a ControlTemplate

DECLINED: This issue is not reproducible with 2016 R3 official release.

Cannot dynamically change the theme of the control.

Implement IsExpandOnDblClickEnabled logic

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

ExpandAll/Collapse issues, Child RadPanelbarItem is resized incorecctly

Second level items cannot be styled to look like first level items.

DECLINED: SecondLevelItemsStyledLikeTopLevelItems SDK sample showing approach to styling PanelBar with more than two levels of PanelBarItems is available since R3 2016 Official Release.
https://github.com/telerik/xaml-sdk/tree/master/PanelBar

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

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 using an ItemContainerStyle on the second(non-root) BarItems, the Background doesn`t apply

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

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

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