I am back with more information. We could easily reproduce the problem on one of our development machines.
AMADEE.Wpf.Designer.exe!AMADEE.Wpf.Designer.App.UnhandledExceptionEventHandler(object sender, System.Windows.Threading.DispatcherUnhandledExceptionEventArgs e) Line 345 C#
WindowsBase.dll!System.Windows.Threading.Dispatcher.CatchException(System.Exception e) + 0x4f bytes
WindowsBase.dll!System.Windows.Threading.Dispatcher.CatchExceptionStatic(object source, System.Exception e) + 0x3d bytes
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.CatchException(object source, System.Exception e, System.Delegate catchHandler) + 0x6b bytes
WindowsBase.dll!MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(object source, System.Delegate method, object args, int numArgs, System.Delegate catchHandler) + 0x93 bytes
WindowsBase.dll!System.Windows.Threading.Dispatcher.InvokeImpl(System.Windows.Threading.DispatcherPriority priority, System.TimeSpan timeout, System.Delegate method, object args, int numArgs) + 0xb4 bytes
WindowsBase.dll!MS.Win32.HwndSubclass.SubclassWndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam) + 0x104 bytes
[Native to Managed Transition]
[Managed to Native Transition]
WindowsBase.dll!MS.Win32.HwndSubclass.DefWndProcWrapper(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam) + 0x50 bytes
[Native to Managed Transition]
[Managed to Native Transition]
WindowsBase.dll!MS.Win32.HwndSubclass.SubclassWndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam) + 0x140 bytes
[Native to Managed Transition]
[Managed to Native Transition]
PresentationFramework.dll!System.Windows.Window.InternalClose(bool shutdown, bool ignoreCancel) + 0xa1 bytes
PresentationFramework.dll!System.Windows.Window.Close() + 0x2a bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.Primitives.RaftingWindow.Close(ActiproSoftware.Windows.Controls.Docking.DockingWindowCloseReason closeReason) + 0x38 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.a(ActiproSoftware.Windows.Controls.Docking.RaftingHost A_0) + 0x94 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.OnDockHostLayoutChanged(object A_0, System.Windows.RoutedEventArgs A_1) + 0x86 bytes
PresentationCore.dll!System.Windows.RoutedEventHandlerInfo.InvokeHandler(object target, System.Windows.RoutedEventArgs routedEventArgs) + 0x7a bytes
PresentationCore.dll!System.Windows.EventRoute.InvokeHandlersImpl(object source, System.Windows.RoutedEventArgs args, bool reRaised) + 0x1ae bytes
PresentationCore.dll!System.Windows.UIElement.RaiseEventImpl(System.Windows.DependencyObject sender, System.Windows.RoutedEventArgs args) + 0x79 bytes
PresentationCore.dll!System.Windows.UIElement.RaiseEvent(System.Windows.RoutedEventArgs e) + 0x29 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.EventNotifier.a() + 0x114 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.DockSite.a(System.Windows.DependencyObject A_0, ActiproSoftware.Windows.Controls.Docking.IDockTarget A_1, ActiproSoftware.Windows.Controls.Docking.Direction A_2) + 0x1bb bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.Primitives.RaftableDockingWindowContainer.OnPreviewWindowExitMove(object A_0, ActiproSoftware.Windows.Controls.Docking.Preview.DockingPreviewEventArgs A_1) + 0x115 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.Preview.PreviewWindow.StopPreview(ActiproSoftware.Windows.Controls.Docking.Preview.DockingPreviewEventArgs A_0) + 0x1a2 bytes
ActiproSoftware.Docking.Wpf351.dll!ActiproSoftware.Windows.Controls.Docking.Preview.PreviewWindow.OnMouseUp(object A_0, System.Windows.Input.MouseButtonEventArgs A_1) + 0x40 bytes
PresentationCore.dll!System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(System.Delegate genericHandler, object genericTarget) + 0x31 bytes
PresentationCore.dll!System.Windows.RoutedEventArgs.InvokeHandler(System.Delegate handler, object target) + 0x36 bytes
PresentationCore.dll!System.Windows.RoutedEventHandlerInfo.InvokeHandler(object target, System.Windows.RoutedEventArgs routedEventArgs) + 0x40 bytes
PresentationCore.dll!System.Windows.EventRoute.InvokeHandlersImpl(object source, System.Windows.RoutedEventArgs args, bool reRaised) + 0x1ae bytes
PresentationCore.dll!System.Windows.UIElement.RaiseEventImpl(System.Windows.DependencyObject sender, System.Windows.RoutedEventArgs args) + 0x79 bytes
PresentationCore.dll!System.Windows.UIElement.RaiseTrustedEvent(System.Windows.RoutedEventArgs args) + 0x41 bytes
PresentationCore.dll!System.Windows.UIElement.RaiseEvent(System.Windows.RoutedEventArgs args, bool trusted) + 0x42 bytes
PresentationCore.dll!System.Windows.Input.InputManager.ProcessStagingArea() + 0x1ff bytes
PresentationCore.dll!System.Windows.Input.InputManager.ProcessInput(System.Windows.Input.InputEventArgs input) + 0x45 bytes
PresentationCore.dll!System.Windows.Input.InputProviderSite.ReportInput(System.Windows.Input.InputReport inputReport) + 0x62 bytes
PresentationCore.dll!System.Windows.Interop.HwndMouseInputProvider.ReportInput(System.IntPtr hwnd, System.Windows.Input.InputMode mode, int timestamp, System.Windows.Input.RawMouseActions actions, int x, int y, int wheel) + 0x263 bytes
PresentationCore.dll!System.Windows.Interop.HwndMouseInputProvider.FilterMessage(System.IntPtr hwnd, MS.Internal.Interop.WindowMessage msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) + 0x4ac bytes
PresentationCore.dll!System.Windows.Interop.HwndSource.InputFilterMessage(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) + 0x75 bytes
WindowsBase.dll!MS.Win32.HwndWrapper.WndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) + 0xbe bytes
WindowsBase.dll!MS.Win32.HwndSubclass.DispatcherCallbackOperation(object o) + 0x7d bytes
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs) + 0x53 bytes
WindowsBase.dll!MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(object source, System.Delegate method, object args, int numArgs, System.Delegate catchHandler) + 0x42 bytes
WindowsBase.dll!System.Windows.Threading.Dispatcher.InvokeImpl(System.Windows.Threading.DispatcherPriority priority, System.TimeSpan timeout, System.Delegate method, object args, int numArgs) + 0xb4 bytes
WindowsBase.dll!MS.Win32.HwndSubclass.SubclassWndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam) + 0x104 bytes
[Native to Managed Transition]
[Managed to Native Transition]
WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrameImpl(System.Windows.Threading.DispatcherFrame frame) + 0xc1 bytes
WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrame(System.Windows.Threading.DispatcherFrame frame) + 0x49 bytes
WindowsBase.dll!System.Windows.Threading.Dispatcher.Run() + 0x4c bytes
PresentationFramework.dll!System.Windows.Application.RunDispatcher(object ignore) + 0x17 bytes
PresentationFramework.dll!System.Windows.Application.RunInternal(System.Windows.Window window) + 0x6f bytes
PresentationFramework.dll!System.Windows.Application.Run(System.Windows.Window window) + 0x26 bytes
PresentationFramework.dll!System.Windows.Application.Run() + 0x1b bytes
AMADEE.Wpf.Designer.exe!AMADEE.Wpf.Designer.App.Main() + 0x5e bytes C#
[Native to Managed Transition]
[Managed to Native Transition]
mscorlib.dll!System.AppDomain.nExecuteAssembly(System.Reflection.RuntimeAssembly assembly, string[] args) + 0x9 bytes
mscorlib.dll!System.Runtime.Hosting.ManifestRunner.Run(bool checkAptModel) + 0x6e bytes
mscorlib.dll!System.Runtime.Hosting.ManifestRunner.ExecuteAsAssembly() + 0x90 bytes
mscorlib.dll!System.Runtime.Hosting.ApplicationActivator.CreateInstance(System.ActivationContext activationContext, string[] activationCustomData) + 0x65 bytes
mscorlib.dll!System.Runtime.Hosting.ApplicationActivator.CreateInstance(System.ActivationContext activationContext) + 0xd bytes
mscorlib.dll!System.Activator.CreateInstance(System.ActivationContext activationContext) + 0x44 bytes
Microsoft.VisualStudio.HostingProcess.Utilities.dll!Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssemblyDebugInZone() + 0x23 bytes
mscorlib.dll!System.Threading.ThreadHelper.ThreadStart_Context(object state) + 0x63 bytes
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool ignoreSyncCtx) + 0xb0 bytes
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) + 0x2c bytes
mscorlib.dll!System.Threading.ThreadHelper.ThreadStart() + 0x44 bytes
[Native to Managed Transition]
Please check the above stack trace maybe you find something. It is quite critical for us as it bombs not only on some specific ToolWindow, we can reproduce it with at least 2 different ones (with various content each)