Hi, I have exactly the same problem. here is my complete code:

<Grid Background="SteelBlue" x:Name="mainGrid">
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="250"/>
        <ColumnDefinition Width="2\*" />
        <ColumnDefinition Width="250" />
    </Grid.ColumnDefinitions>
    
    <Grid.RowDefinitions>
        <RowDefinition />
        <RowDefinition Height="25" />
    </Grid.RowDefinitions> 
    
    <Border BorderThickness="4" BorderBrush="SteelBlue"  Background="White">
        <WFDesigner:WorkflowListView x:Name="WorkflowList" Margin="10"/>
    </Border>
    
    <WFDesigner:WorkflowDetailView x:Name="WorkflowDetail" Margin="0,4" Grid.Column="1" Background="White"/>
    
    <GridSplitter HorizontalAlignment="Right" Grid.Column="1" ResizeBehavior="CurrentAndNext" Width="4" Background="Red" />
    
    <Border BorderThickness="0,4,4,4" BorderBrush="SteelBlue"  Grid.Column="2" Background="White">
        <Grid x:Name="ToolboxProperties" DockPanel.Dock="Right">
            <Grid.RowDefinitions>
                <RowDefinition Height="2\*" />
                <RowDefinition Height="1\*" />
            </Grid.RowDefinitions>
            <ContentControl Content="{Binding ToolboxControl}"/>
            <ContentControl DataContext="{Binding SelectedItem}" Content="{Binding Designer.PropertyInspectorView}" Grid.Row="1"/>
        </Grid>
    </Border>
    
    <StatusBar Grid.Row="1" Grid.ColumnSpan="3" >
        <TextBlock Text="{Binding Status}" Margin="5,0" />
    </StatusBar>
</Grid>

I tried overriding it by setting "Cursor" value in the GridSplitter XAML definition but it didn't work. Any idea?