 <p>What's happening is the Dependency Property is getting Registered multiple times under the same name and owner. Dependency Properties are intended to have a single owner, and should be statically instanced. If you don't statically instance them, an attempt will be made to register them for each instance of the control.</p> <p><strong>Make your DependencyProperty declaration static. Change it from:</strong></p> <pre><code> public DependencyProperty SomeStringValueProperty = DependencyProperty.Register("SomeStringValue", typeof(string), typeof(ExampleUserControl)); </code></pre> <p><strong>To:</strong></p> <pre><code>public static DependencyProperty SomeStringValueProperty = DependencyProperty.Register("SomeStringValue", typeof(string), typeof(ExampleUserControl)); </code></pre>