AttachedDropShadow overridden by ImageEx Stretch="UniformToFill"

DropShadowPanel works well

 <Grid>
        <StackPanel>
            <Grid x:Name="imgGrid" Width="300" Height="300">
                <Grid x:Name="ShadowTarget"/>
                <controls:ImageEx x:Name="img" Stretch="UniformToFill" EnableLazyLoading="True" Padding="0 0 3 4" Source="ms-appx:///Assets/pineapple.jpg">
                    <tkUI:Effects.Shadow>
                        <tkUI:AttachedDropShadow BlurRadius="8" IsMasked="True"
                                   CornerRadius="2"
                                   Color="Black"
                                   Offset="3,4"
                                   Opacity="1"
                                   CastTo="{Binding ElementName=ShadowTarget}"/>
                    </tkUI:Effects.Shadow>
                </controls:ImageEx>
            </Grid>

            <controls:DropShadowPanel x:Name="imgPnl" BlurRadius="8" Margin="0 10 3 4" Width="300" Height="300"
                                ShadowOpacity="1"
                                OffsetX="3"
                                OffsetY="4"
                                Color="Black"
                                VerticalAlignment="Stretch"
                                HorizontalAlignment="Stretch"
                                IsMasked="False">
                <controls:ImageEx Stretch="UniformToFill" EnableLazyLoading="True"  Source="ms-appx:///Assets/pineapple.jpg"/>
            </controls:DropShadowPanel>
        </StackPanel>
    </Grid>

Expected behavior

AttachedDropShadow works like DropShadowPanel

Screenshots