I am also seeing this error in the latest service release of 2014.2

I will try to upgrade to 2015.1 but I am not hopeful if the bug has been around since 2012.  Is there some workaround ?

 Greg

2015-04-22 9:05:48 PM Application_ThreadException():System.NullReferenceException: Object reference not set to an instance of an object.
   at Infragistics.Win.UltraWinGrid.UltraGridBand.ResizeLayoutItemHelper(UIElement elem, ILayoutItem resizeItem, Size containerSize, Size itemTargetSize, Point delta, Boolean raiseResizeNotification, Boolean modifyWidthDimension, Boolean modifyHeightDimension)
   at Infragistics.Win.UltraWinGrid.UltraGridBand.ResizeLayoutItem(UIElement elem, ILayoutItem resizeItem, Size containerSize, Point delta)
   at Infragistics.Win.UltraWinGrid.UltraGridBand.ResizeLayoutItem(ILayoutItem resizeItem, Size containerSize, Point delta)
   at Infragistics.Win.UltraWinGrid.HeaderUIElement.ApplyAdjustment(Point delta)
   at Infragistics.Win.AdjustableUIElement.OnMouseUp(MouseEventArgs e)
   at Infragistics.Win.UltraWinGrid.HeaderUIElement.OnMouseUp(MouseEventArgs e)
   at Infragistics.Win.ControlUIElementBase.ProcessMouseUpHelper(Object sender, MouseEventArgs e)
   at Infragistics.Win.ControlUIElementBase.ProcessMouseUp(Object sender, MouseEventArgs e)
   at Infragistics.Win.Utilities.ProcessEvent(Control control, ProcessEvent eventToProcess, EventArgs e)
   at Infragistics.Win.UltraControlBase.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.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)