I made changes which also caused changes to be made to files in a submodule I am referencing. In SourceTree I opened up the view for the submodule, and clicked on a file in the "Working Copy Changes" pane. I then pressed the down key to go to the next file and the application crashed. From the log file:
2013-08-28T14:19:45: Fatal error:
System.InvalidOperationException: Operation is not valid due to the current state of the object.

2013-08-28T14:19:45: Stack trace:
at SourceTree.View.Utils.ScrollableTabPanel.LineDown()
at System.Windows.Controls.ScrollViewer.ExecuteNextCommand()
at System.Windows.Controls.ScrollViewer.OnLayoutUpdated(Object sender, EventArgs e)
at System.Windows.ContextLayoutManager.fireLayoutUpdateEvent()
at System.Windows.ContextLayoutManager.UpdateLayout()
at System.Windows.Controls.ScrollViewer.OnKeyDown(KeyEventArgs e)
at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
at System.Windows.Input.InputManager.ProcessStagingArea()
at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
at System.Windows.Interop.HwndKeyboardInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawKeyboardActions actions, Int32 scanCode, Boolean isExtendedKey, Boolean isSystemKey, Int32 virtualKey)
at System.Windows.Interop.HwndKeyboardInputProvider.ProcessKeyAction(MSG& msg, Boolean& handled)
at System.Windows.Interop.HwndSource.CriticalTranslateAccelerator(MSG& msg, ModifierKeys modifiers)
at System.Windows.Interop.HwndSource.OnPreprocessMessage(Object param)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)