>I think I'm breaking your code. Don't have more time to play with it right now, but here's what I have:
>
>XAML:

><Window x:Class="WpfPropertyInheritance.Window1"
>    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
>    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
>    xmlns:loc="clr-namespace:WpfPropertyInheritance"
>    Title="Window1" Height="300" Width="300">
>    <StackPanel>
>    <Button Height="23" Name="button1" Width="75" Click="button1_Click">Button</Button>
>    <Button Height="23" Name="button2" Width="75" Click="button2_Click">Button</Button>
>    <loc:ShapeCanvas3 x:Name="scTest" Height="172">
>      <StackPanel Canvas.Left="46" Canvas.Top="38" Height="100" Name="spnlTest" Width="200" >
>        <Rectangle Height="100" Name="rectangle1" Stroke="Black" Width="200" Fill="Azure" />
>      </StackPanel>
>    </loc:ShapeCanvas3>
>  </StackPanel>
></Window>
>

>
>C#:

using System.Windows;
>using System.Windows.Controls;
>using System.Diagnostics;
>
>namespace WpfPropertyInheritance
>  {
>  /// <summary>
>  /// Interaction logic for Window1.xaml
>  /// </summary>
>  public partial class Window1 : Window
>    {
>    public Window1()
>      {
>      InitializeComponent();
>      }
>
>    private void button1_Click(object sender, RoutedEventArgs e)
>      {
>      Debug.WriteLine("A1 Starting Value: " + scTest.ContentIsLocked.ToString());
>      scTest.ContentIsLocked = true;
>      Debug.WriteLine("A2 Set Canvas True: " + scTest.ContentIsLocked.ToString());
>      scTest.ContentIsLocked = true;
>      Debug.WriteLine("A3 Set Canvas True Again: " + scTest.ContentIsLocked.ToString());
>      scTest.ContentIsLocked = false;
>      Debug.WriteLine("A4 Set Canvas False: " + scTest.ContentIsLocked.ToString());
>      }
>
>    private void button2_Click(object sender, RoutedEventArgs e)
>      {
>      Debug.WriteLine("B2 Starting Values: " + scTest.ContentIsLocked.ToString()+ ":" + rectangle1.GetValue(ShapeCanvas3.ContentIsLockedProperty).ToString());
>      scTest.ContentIsLocked = true;
>      Debug.WriteLine("B2 Set Canvas True: " + scTest.ContentIsLocked.ToString() + ":" + rectangle1.GetValue(ShapeCanvas3.ContentIsLockedProperty).ToString());
>      rectangle1.SetValue(ShapeCanvas3.ContentIsLockedProperty, false);
>      Debug.WriteLine("B2 Set Rect False: " + scTest.ContentIsLocked.ToString() + ":" + rectangle1.GetValue(ShapeCanvas3.ContentIsLockedProperty).ToString());
>      }
>    }
>
>  public class ShapeCanvas3 : Canvas
>    {
>    public static DependencyProperty ContentIsLockedProperty;
>
>    static ShapeCanvas3()
>      {
>      FrameworkPropertyMetadata p = new FrameworkPropertyMetadata(
>        new PropertyChangedCallback(OnContentIsLockedChanged), 
>        new CoerceValueCallback(CoerceIsLocked)
>        );
>      p.Inherits = true;
>      ContentIsLockedProperty = DependencyProperty.RegisterAttached("ContentIsLocked", typeof(bool), typeof(ShapeCanvas3), p);
>      }
>
>    public bool ContentIsLocked
>      {
>      set {
>          Debug.WriteLine("SetVal: " + value.ToString());
>          if (value)
>            SetValue(ContentIsLockedProperty, value);
>          else
>            this.ClearValue(ContentIsLockedProperty);
>          }
>      get { return (bool)GetValue(ContentIsLockedProperty); }
>      }
>
>    private static void OnContentIsLockedChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
>      {
>      }
>
>    private static object CoerceIsLocked(DependencyObject d, object value)
>      {
>      if (d.ReadLocalValue(ContentIsLockedProperty) == DependencyProperty.UnsetValue)
>        {
>        Debug.WriteLine("Coerce 1: "+d.ToString()+":" + value.ToString());
>        return value;
>        }
>      bool b = (bool)value;
>      if (b)
>        {
>        Debug.WriteLine("Coerce 2: " + b.ToString());
>        return b;
>        }
>      else
>        {
>        Debug.WriteLine("Coerce 3: UnsetValue");
>        return DependencyProperty.UnsetValue;
>        }
>      }
>    
>    }  
>  }

>
>Here is the debug output on the second button:
>
>

>B2 Starting Values: False:False
>SetVal: True  
>Coerce 1: WpfPropertyInheritance.ShapeCanvas3:True
>Coerce 1: System.Windows.Controls.StackPanel:True
>Coerce 1: System.Windows.Shapes.Rectangle:True
>B2 Set Canvas True: True:True
>Coerce 1: System.Windows.Shapes.Rectangle:False
>B2 Set Rect False: True:False
>

>
>B2 Set Rect False: True:False = Canvas is locked, but child was able to be unlocked.
>
>Am I missing something?

Hi,
I'm dragged back into VFP/ASP.NET for a couple of days so I can't try your version at the mo.....
I'll get back to you ASAP,
Viv