Can't get CommandTarget in WPF

Question

Say, I have the following XAML:

<r:RibbonWindow x:Class="WPFApp.Root"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:r="urn:fluent-ribbon"
        xmlns:local="clr-namespace:WPFApp"
        mc:Ignorable="d"
        WindowStartupLocation="CenterScreen"
        Title="FL Query" Height="450" Width="800">

  <Window.CommandBindings>
    <CommandBinding Command="ApplicationCommands.Copy" Executed="OnCopy"/>
  </Window.CommandBindings>
  
  <Grid>
    <Grid.RowDefinitions>
      <RowDefinition Height="Auto"/>
      <RowDefinition/>
    </Grid.RowDefinitions>

    <r:Ribbon Grid.Row="0">

      <r:RibbonTabItem Header="Home">
        <r:RibbonGroupBox Header="ID">
          <r:TextBox x:Name="txtID" Header="ID:" Width="100"/>
          <r:Button Size="Large"
                    LargeIcon="pack://application:,,,/WPFApp;component/img/Run.png" 
                    Click="OnAction">
                    Content="Run"/>
        </r:RibbonGroupBox>
      </r:RibbonTabItem>

    </r:Ribbon>

    <Grid Grid.Row="1">
      <Label x:Name="lbl">
        <Label.ContextMenu>
          <ContextMenu>
            <MenuItem Command="ApplicationCommands.Copy"
                      CommandTarget="{Binding ElementName=lbl}"/>
          </ContextMenu>
        </Label.ContextMenu>
      </Label>
    </Grid>

  </Grid>
</r:RibbonWindow>

Upon pressing Run button I retrieve ID number from database and put it to label. Then I'm trying to copy label's text (i.e. this ID) with label's context menu by using CommandTarget. However, e.Source holds reference to previously pressed Run button:

private void OnCopy(object sender, ExecutedRoutedEventArgs e)
{
  // sender = WPFApp.Root
  // e.Source = Fluent.Ribbon
  // e.OriginalSource = class "Fluent.Button": Header = "Run", Size = Large, IsSimplified = false
    
  // label is NULL here
  var label = e.Source as Label;
  Clipboard.SetText(label.Content.ToString());
}

Why CommandTarget doesn't work? Why do I get Button (Run) instead of a label?