Using custom panel window dragging works only in the first line

Hi,

we are using custom panel for multiline tab header, while using custom panel window dragging works only in the first line.

In this sample unable to drag and drop document window ("Main 12") in between "Main 10" & "Main 9"

<Window x:Class="WpfApplication4.MainWindow"
        xmlns:docking="http://schemas.actiprosoftware.com/winfx/xaml/docking"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="300">
    <Grid>
        <docking:DockSite x:Name="dockSiteObj" ItemContainerRetentionMode="Wrapped">
            <docking:SplitContainer>
                <docking:Workspace>
                    <docking:TabbedMdiHost x:Name="tabbedMdiHost" TabPlacement="Bottom" >
                        <docking:TabbedMdiContainer Background="AntiqueWhite" TabOverflowBehavior="None">
                            <docking:DocumentWindow Title="Main 1" />
                            <docking:DocumentWindow Title="Main 2" />
                            <docking:DocumentWindow Title="Main 3" />
                            <docking:DocumentWindow Title="Main 4" />
                            <docking:DocumentWindow Title="Main 5" />
                            <docking:DocumentWindow Title="Main 6" />
                            <docking:DocumentWindow Title="Main 7" />
                            <docking:DocumentWindow Title="Main 8" />
                            <docking:DocumentWindow Title="Main 9" />
                            <docking:DocumentWindow Title="Main 10"/>
                            <docking:DocumentWindow Title="Main 11"/>
                            <docking:DocumentWindow Title="Main 12"/>
                            <docking:TabbedMdiContainer.Style>
                                <Style TargetType="docking:TabbedMdiContainer">
                                    <Setter Property="ItemsPanel">
                                        <Setter.Value>
                                            <ItemsPanelTemplate>
                                                <WrapPanel Orientation="Horizontal"/>
                                            </ItemsPanelTemplate>
                                        </Setter.Value>
                                    </Setter>
                                </Style>
                            </docking:TabbedMdiContainer.Style>
                        </docking:TabbedMdiContainer>
                    </docking:TabbedMdiHost>
                </docking:Workspace>
            </docking:SplitContainer>
        </docking:DockSite>
    </Grid>
</Window>

 Is there any way to solve this issue?

Thanks