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.

Expose a property to easily control the expander indicator style and visibility.

From Q1 2016 SP users will able to use the ExpanderStyle property of the RadpanelBarItem in order to style the arrow expander.

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.

Allow resizing of PanelBarItems. http://www.telerik.com/community/forums/wpf/panelbar/resize-capabilities-to-radpanelbaritems.aspx

Implement IsExpandOnDblClickEnabled logic

Possbility to have PanelBarItems with fixed height and other PanelBarItems that take the rest of the available height equally

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

Make expand animation to be horizontal when Orientation is Horizontal.

DECLINED: Cannot reproduce with R3 2016 binaries.

Add an Icon property to allow displaying images in the RadPanelBarItem Header.

Declined:

Adding such property requires also adding a visual element (Image) in the Template of the RadPanelBarItems.
RadTreeView also has Image in its ControlTemplate and we have to admit this was our design mistake in the past. Such element makes the Style larger, makes the virtualization harder to support, slows down the performance.

How To Add Image in RadPanelBar:

In non-databound scenarios just add the Image in the Header:

      <telerik:RadPanelBarItem>
                <telerik:RadPanelBarItem.Header>
                    <StackPanel>
                        <Image Source="MyImage.png" Margin="5"/>
                        <TextBlock Text="{Binding Name}" />
                    </StackPanel>
                </telerik:RadPanelBarItem.Header>
            </telerik:RadPanelBarItem>

In databound scenario set the ItemTemplate of the RadPanelBar:

DataTemplate x:Key="itemTemplate">
                <StackPanel>
                    <Image Source="MyImage.png" Margin="5"/>
                    <TextBlock Text="{Binding Name}" />
                </StackPanel>
            </DataTemplate>

 <telerik:RadPanelBar ItemTemplate="{StaticResource itemTemplate}"/>

See the SDK example demonstrating those approaches: https://github.com/telerik/xaml-sdk/tree/master/PanelBar/AddHeaderIcon

ExpandAll/Collapse issues, Child RadPanelbarItem is resized incorecctly