copying the text in a plugin generates an error

Copying the text in some plugins generates an error (see attached document)

System.InvalidOperationException: Impossible de sérialiser un type non public 'MdXaml.MarkdownScrollViewer+OpenCommand'.
à System.Windows.Markup.Primitives.MarkupWriter.VerifyTypeIsSerializable(Type type)
à System.Windows.Markup.Primitives.MarkupWriter.WriteItem(MarkupObject item)
à System.Windows.Markup.Primitives.MarkupWriter.SaveAsXml(XmlWriter writer, MarkupObject item)
à System.Windows.Markup.XamlWriter.Save(Object obj)
à System.Windows.Documents.TextRangeSerialization.WriteComplexProperties(XmlWriter xmlWriter, DependencyObject complexProperties, Type elementType)
à System.Windows.Documents.TextRangeSerialization.WriteStartXamlElement(ITextRange range, ITextPointer textReader, XmlWriter xmlWriter, XamlTypeMapper xamlTypeMapper, Boolean reduceElement, Boolean preserveTextElements)
à System.Windows.Documents.TextRangeSerialization.WriteXamlTextSegment(XmlWriter xmlWriter, ITextPointer rangeStart, ITextPointer rangeEnd, XamlTypeMapper xamlTypeMapper, Int32& elementLevel, WpfPayload wpfPayload, Boolean ignoreWriteHyperlinkEnd, List`1 ignoreList, Boolean preserveTextElements)
à System.Windows.Documents.TextRangeSerialization.WriteXaml(XmlWriter xmlWriter, ITextRange range, Boolean useFlowDocumentAsRoot, WpfPayload wpfPayload, Boolean preserveTextElements)
à System.Windows.Documents.WpfPayload.SaveRange(ITextRange range, Stream& stream, Boolean useFlowDocumentAsRoot, Boolean preserveTextElements)
à System.Windows.Documents.TextEditorCopyPaste._CreateDataObject(TextEditor This, Boolean isDragDrop)
à System.Windows.Documents.TextEditorCopyPaste.Copy(TextEditor This, Boolean userInitiated)
à System.Windows.Input.CommandBinding.OnExecuted(Object sender, ExecutedRoutedEventArgs e)
à System.Windows.Input.CommandManager.ExecuteCommandBinding(Object sender, ExecutedRoutedEventArgs e, CommandBinding commandBinding)
à System.Windows.Input.CommandManager.FindCommandBinding(Object sender, RoutedEventArgs e, ICommand command, Boolean execute)
à System.Windows.Input.CommandManager.OnExecuted(Object sender, ExecutedRoutedEventArgs e)
à System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
à System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
à System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
à System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
à System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
à System.Windows.Input.RoutedCommand.ExecuteImpl(Object parameter, IInputElement target, Boolean userInitiated)
à System.Windows.Input.CommandManager.TranslateInput(IInputElement targetElement, InputEventArgs inputEventArgs)
à System.Windows.UIElement.OnKeyDownThunk(Object sender, KeyEventArgs e)
à System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
à System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
à System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
à System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
à System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
à System.Windows.Input.InputManager.ProcessStagingArea()
à System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
à System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
à System.Windows.Interop.HwndKeyboardInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawKeyboardActions actions, Int32 scanCode, Boolean isExtendedKey, Boolean isSystemKey, Int32 virtualKey)
à System.Windows.Interop.HwndKeyboardInputProvider.ProcessKeyAction(MSG& msg, Boolean& handled)
à System.Windows.Interop.HwndSource.CriticalTranslateAccelerator(MSG& msg, ModifierKeys modifiers)
à System.Windows.Interop.HwndSource.OnPreprocessMessage(Object param)
à System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
à System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)

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