FluidMoveBehavior in Toolbar

We tried to have a FluidMoveBehaviour in a Toolbar. But it does not work. This is how it looks like:

<ToolBar DataContext="{Binding MostRecentlyUsed}"
                         HeaderTemplate="{StaticResource RotatedToolbarHeaderTemplate}"
                         ItemsSource="{Binding Items}"><ToolBar.Header><TextBlock FontSize="{StaticResource ToolBarHeaderFontSize}"
                                   Foreground="{StaticResource {x:Static SystemColors.ControlDarkDarkBrushKey}}"><Run Text="{x:Static prop:Resources.ToolBarHeader_Recent}" /></TextBlock></ToolBar.Header><ToolBar.ItemsPanel><ItemsPanelTemplate><WrapPanel  ><i:Interaction.Behaviors><ei:FluidMoveBehavior AppliesTo="Children"
                                                          Duration="0:0:0.5"
                                                          InitialTag="DataContext"
                                                          Tag="DataContext"><ei:FluidMoveBehavior.EaseY><CubicEase EasingMode="EaseInOut" /></ei:FluidMoveBehavior.EaseY><ei:FluidMoveBehavior.EaseX><CubicEase EasingMode="EaseInOut" /></ei:FluidMoveBehavior.EaseX></ei:FluidMoveBehavior></i:Interaction.Behaviors></WrapPanel ></ItemsPanelTemplate></ToolBar.ItemsPanel></ToolBar>