title: Changing states of checkbox with even trigger
body: <p>I have this <code>CheckBox</code>:</p>
  
  <pre><code>&lt;CheckBox x:Name="checkNotAppointed" Grid.Column="1" Grid.Row="2" Content="Not Appointed" &gt;
      &lt;CheckBox.Style&gt;
          &lt;Style TargetType="{x:Type CheckBox}"&gt;
              &lt;Setter Property="Margin" Value="2" /&gt;
              &lt;Setter Property="IsEnabled" Value="True" /&gt;
              &lt;Setter Property="IsChecked" Value="{Binding FilterForNotAppointed, UpdateSourceTrigger=PropertyChanged}" /&gt;
              &lt;Style.Triggers&gt;
                  &lt;MultiDataTrigger&gt;
                      &lt;MultiDataTrigger.Conditions&gt;
                          &lt;Condition Binding="{Binding IsChecked, ElementName=checkElder}" Value="True" /&gt;
                          &lt;Condition Binding="{Binding IsChecked, ElementName=checkMinisterialServant}" Value="False" /&gt;
                      &lt;/MultiDataTrigger.Conditions&gt;
                      &lt;Setter Property="IsEnabled" Value="True" /&gt;
                  &lt;/MultiDataTrigger&gt;
                  &lt;MultiDataTrigger&gt;
                      &lt;MultiDataTrigger.Conditions&gt;
                          &lt;Condition Binding="{Binding IsChecked, ElementName=checkElder}" Value="False" /&gt;
                          &lt;Condition Binding="{Binding IsChecked, ElementName=checkMinisterialServant}" Value="True" /&gt;
                      &lt;/MultiDataTrigger.Conditions&gt;
                      &lt;Setter Property="IsEnabled" Value="True" /&gt;
                  &lt;/MultiDataTrigger&gt;
                  &lt;MultiDataTrigger&gt;
                      &lt;MultiDataTrigger.Conditions&gt;
                          &lt;Condition Binding="{Binding IsChecked, ElementName=checkElder}" Value="False" /&gt;
                          &lt;Condition Binding="{Binding IsChecked, ElementName=checkMinisterialServant}" Value="False" /&gt;
                      &lt;/MultiDataTrigger.Conditions&gt;
                      &lt;Setter Property="IsChecked" Value="True" /&gt;
                      &lt;Setter Property="IsEnabled" Value="False" /&gt;
                  &lt;/MultiDataTrigger&gt;
              &lt;/Style.Triggers&gt;
          &lt;/Style&gt;
      &lt;/CheckBox.Style&gt;
  &lt;/CheckBox&gt;
  </code></pre>
  
  <p>If I untick either <code>checkElder</code> or <code>checkMinisterialServant</code> it has no affect on <code>checkNotAppointed</code>. Correct.</p>
  
  <p>If I then untick both of them, it checks the <code>checkNotAppointed</code> and disables. Correct.</p>
  
  <p>If I then check one of the other two, it enables <code>checkNotAppointed</code> but always unchecks it. Why?</p>