Closing unactive pane closes selected pane

[A]

Hi Telerik,

This might be an obvious question but I'd like to ask this anyway. I have two RadDocumentPanes, I'd like to close the inactive pane (that's pane B, see Sample.png) by clicking the close button. But the pane being closed is the selected/active pane  (that's pane A).

My Code:

                <telerik:RadButton x:Name="CloseButton"
                        Grid.Column="4"
                        Command="telerik:RadDockingCommands.Close"
                        Style="{StaticResource CustomRadButtonDocumentCloseStyle}"
                        Visibility="{Binding IsEnabled, RelativeSource={RelativeSource Self}, Converter={StaticResource BooleanToVisibilityConverter}}"/>