Object not set to an instance of an object when editing a WPF datagrid combobox column when the column is sorted

Question

I have a Datagrid in which I use a TextColumn bound to an Integer Property.I can edit the the values in the TextColumn allright until I click the column header. The column will sort correctly when clicked but when I then try to edit a value afterwards I get an exception when I cause a LostFocus Event by clicking somewhere else.

(Question changed to the minimal required setup to make it reproducible)

The XAML:

<DataGridTextColumn Binding="{Binding CompStrength}"/>

The StackTrace:

bij System.Windows.Controls.DataGrid.UpdateRowEditing(DataGridCell cell)
bij System.Windows.Controls.DataGrid.OnExecutedCommitEdit(ExecutedRoutedEventArgs e)
bij System.Windows.Controls.DataGrid.OnExecutedCommitEdit(Object sender, ExecutedRoutedEventArgs e)
bij System.Windows.Input.CommandBinding.OnExecuted(Object sender, ExecutedRoutedEventArgs e)
bij System.Windows.Input.CommandManager.ExecuteCommandBinding(Object sender, ExecutedRoutedEventArgs e, CommandBinding commandBinding)
bij System.Windows.Input.CommandManager.FindCommandBinding(CommandBindingCollection commandBindings, Object sender, RoutedEventArgs e, ICommand command, Boolean execute)
bij System.Windows.Input.CommandManager.FindCommandBinding(Object sender, RoutedEventArgs e, ICommand command, Boolean execute)
bij System.Windows.Input.CommandManager.OnExecuted(Object sender, ExecutedRoutedEventArgs e)
bij System.Windows.UIElement.OnExecutedThunk(Object sender, ExecutedRoutedEventArgs e)
bij System.Windows.Input.ExecutedRoutedEventArgs.InvokeEventHandler(Delegate genericHandler, Object target)
bij System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
bij System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
bij System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
bij System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
bij System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted)
bij System.Windows.Input.RoutedCommand.ExecuteImpl(Object parameter, IInputElement target, Boolean userInitiated)
bij System.Windows.Input.RoutedCommand.Execute(Object parameter, IInputElement target)
bij System.Windows.Controls.DataGrid.EndEdit(RoutedCommand command, DataGridCell cellContainer, DataGridEditingUnit editingUnit, Boolean exitEditMode)
bij System.Windows.Controls.DataGrid.OnCurrentCellChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
bij System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
bij System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
bij System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
bij System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
bij System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
bij System.Windows.DependencyObject.SetCurrentValueInternal(DependencyProperty dp, Object value)
bij System.Windows.Controls.DataGrid.set_CurrentCellContainer(DataGridCell value)
bij System.Windows.Controls.DataGrid.set_FocusedCell(DataGridCell value)
bij System.Windows.Controls.DataGridCell.OnAnyGotFocus(Object sender, RoutedEventArgs e)
bij System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
bij System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
bij System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
bij System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
bij System.Windows.FrameworkElement.OnGotFocus(RoutedEventArgs e)

Answer 1

I finally tracked down the cause for this exception after painstakingly rebuilding the project: Surprisingly the error appears after adding the classc.xaml theme from PresentationFramework.Classic.dll as a resource to the WPF project. I contacted Microsoft about this en we'll see what happens...