Problem with EventTrigger for MouseUp, it triggers only on right-button

Question

Please take a look at the following snippet:

<EventTrigger RoutedEvent="Image.MouseUp">
    <BeginStoryboard>
        <Storyboard>
            <DoubleAnimation
            Storyboard.TargetName="TranslateTransform"
            Storyboard.TargetProperty="X"
            From="1" To="0" Duration="0:0:0.15"
        />
            <DoubleAnimation
            Storyboard.TargetName="TranslateTransform"
            Storyboard.TargetProperty="Y"
            From="1" To="0" Duration="0:0:0.15"
        />
        </Storyboard>
    </BeginStoryboard>
</EventTrigger>
<EventTrigger RoutedEvent="Image.MouseDown">
    <BeginStoryboard>
        <Storyboard>
            <DoubleAnimation
            Storyboard.TargetName="TranslateTransform"
            Storyboard.TargetProperty="X"
            From="0" To="1" Duration="0:0:0.15"
        />
            <DoubleAnimation
            Storyboard.TargetName="TranslateTransform"
            Storyboard.TargetProperty="Y"
            From="0" To="1" Duration="0:0:0.15"
        />
        </Storyboard>
    </BeginStoryboard>
</EventTrigger>

The MouseDown trigger works great. The MouseUp trigger works only on Right-Click.

Weird no? Any ideas!?