c# - Polygon Animation won't work in c#

Question

I am having a small Problem in C#. I want to have a Polygon I drew in WPF to be animated on hover. I successfully drew the polygon like this:

 <Polygon  Fill="#FF767676" Points="0,8,12,0,12,16" Margin="30" Style="{DynamicResource BackAndForth}"/>

I then defined a style

    <Style x:Key="BackAndForth" TargetType="{x:Type Polygon}">
        <Setter Property="Opacity" Value="0.6" />
        <Style.Triggers>
            <Trigger Property="IsMouseOver" Value="True">
                <Trigger.EnterActions>
                    <BeginStoryboard>
                        <Storyboard>
                            <DoubleAnimation  Duration="0:0:0.2" Storyboard.TargetProperty="Opacity" From="0.6"  To="1" />
                        </Storyboard>
                    </BeginStoryboard>
                </Trigger.EnterActions>
                <Trigger.ExitActions>
                    <BeginStoryboard>
                        <Storyboard>
                            <DoubleAnimation  Duration="0:0:0.2" Storyboard.TargetProperty="Opacity" From="1" To="0.6" />
                        </Storyboard>
                    </BeginStoryboard>
                </Trigger.ExitActions>
            </Trigger>
        </Style.Triggers>
    </Style>

Somehow this won't work. The setter property in line 2 works. But somehow the animation won't get triggered. I already looked it up but polygons have a IsMouseOver Property.

The exact same code works perfecty on buttons (with a proper target type).

Any ideas what I am missing?