Trouble adding second EventTriggerBehavior to control - UWP

Question

In a user control I have this:

        <ToggleButton x:Name="toggleButton" Style="{StaticResource PaneToggleButton}"
                      Content="{Binding MyChromaticNotes.Root.Note}">
            <Interactivity:Interaction.Behaviors>
                <Core:EventTriggerBehavior EventName="Checked">
                    <Core:InvokeCommandAction
                        Command="{Binding AddSelectedCommand}" />
                </Core:EventTriggerBehavior>

                <Core:EventTriggerBehavior EventName="UnChecked">
                    <Core:InvokeCommandAction
                        Command="{Binding RemoveSelectedCommand}"/>
                </Core:EventTriggerBehavior>
            </Interactivity:Interaction.Behaviors>

        </ToggleButton>

The two commands are binding to my view-model's static properties of type 'DelegateCommand' which implements ICommand. In the view model constructor, I have this:

        #region Add Selected
        AddSelectedCommand = new DelegateCommand(
            () => { SelectedTones.Add(MyChromaticNotes.Root.Note); },
            () => { return true; }
            );
        #endregion
        #region Remove Selected
        RemoveSelectedCommand = new DelegateCommand(
            () => { SelectedTones.Remove(MyChromaticNotes.Root.Note); },
            () => { return SelectedTones.Contains(MyChromaticNotes.Root.Note); }
            );
        #endregion

If I try to run it I get "Cannot add instance of 'EventTriggerBehavior' to collection of type BehaviorCollection" on the Output Window, but if I remove the second 'EventTriggerBehavior' from the XAML and the corresponding RemoveSelectedCommand DelegateCommand from the view model It runs and I can Add to SelectedTones (of type ObservableCollection).

Question: Why is the second EventTriggerBehavior not working, how to fix?

Answer 1

The event name is Unchecked not UnChecked.

Casing matters.