If I have a pane that starts out DockedLeft and I drag that pane to now be floating, when I go to redock it at the original dock location of DockedLeft or to a new dock location of DockedTop, I get the following error:

System.NullReferenceException was unhandled
  Message="Object reference not set to an instance of an object."
  Source="Infragistics2.Win.UltraWinDock.v8.3"
  StackTrace:
       at Infragistics.Win.UltraWinDock.TabManagerBase.get_InterTabSpacing()
       at Infragistics.Win.UltraWinDock.TabManagerBase.Infragistics.Win.UltraWinTabs.ITabProvider.get_InterTabSpacing()
       at Infragistics.Win.UltraWinTabs.TabManager.get_InterTabSpacingResolved()
       at Infragistics.Win.UltraWinTabs.TabManager.InitializeFirstDisplayedTabItem(ITabItem tab, ScrollType scrollType, Int32 scrollIncrement, Boolean fireScrollEvents)
       at Infragistics.Win.UltraWinTabs.TabManager.VerifyFirstDisplayedTabItem()
       at Infragistics.Win.UltraWinTabs.TabManager.VerifyMetrics()
       at Infragistics.Win.UltraWinTabs.TabManager.GetRequiredSize()
       at Infragistics.Win.UltraWinTabs.TabManager.GetRequiredExtent()
       at Infragistics.Win.UltraWinDock.UnpinnedTabArea.UpdateSize()
       at Infragistics.Win.UltraWinDock.UnpinnedTabArea.AddUnpinnedPane(DockableControlPane pane)
       at Infragistics.Win.UltraWinDock.UnpinnedTabArea.ProcessRemovedGroupPane(DockableGroupPane group)
       at Infragistics.Win.UltraWinDock.UltraDockManager.FixUnpinnedAreasForRemovedGroup(DockableGroupPane oldGroup)
       at Infragistics.Win.UltraWinDock.UltraDockManager.RemoveUnreferencedGroupPanes()
       at Infragistics.Win.UltraWinDock.UltraDockManager.RemoveUnreferencedDockAreasHelper()
       at Infragistics.Win.UltraWinDock.UltraDockManager.RemoveUnreferencedDockAreas()
       at Infragistics.Win.UltraWinDock.UltraDockManager.ResumeLayout()
       at Infragistics.Win.UltraWinDock.DropLocation.ProcessDrop()
       at Infragistics.Win.UltraWinDock.DragManager.EndDrag()
       at Infragistics.Win.UltraWinDock.DragManager.ProcessMouseUp(MouseEventArgs e)
       at Infragistics.Win.UltraWinDock.DragManager.MouseUp(MouseEventArgs e)
       at Infragistics.Win.UltraWinDock.DockControlBase.OnMouseUp(MouseEventArgs e)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
       at System.Windows.Forms.ContainerControl.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(ApplicationContext context)
       at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
       at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
       at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[ commandLine)
       at GMSB.My.MyApplication.Main(String[ Args) in 17d14f5c-a337-4978-8281-53493378c1071.vb:line 81
       at System.AppDomain._nExecuteAssembly(Assembly assembly, String[ args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[ args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException:

It doesn't point to a particular line of code in my app, so I'm not sure how to resolve this issue.