System.Exception is raised on inserting RTF content located before a newly created bookmark

Hi - since updating my application to 15.1.7 and rolling it out to our customers (we have several hundred sites) we're seeing error reports coming back from users showing a problem with the XtraRichEdit control.

We are using the XtraRichEdit control as an editor for composing emails. The feature which is throwing the exception is when a user tries to insert their email signature, which is just a string of RTF DATA which itself is created using a DevEx XtraRichEdit control.

Here's our code which has not changed and has worked for months without any problem :-

C#
DocumentRange InsertSignature(string rtfdata)  
{  
  if (String.IsNullOrEmpty(rtfdata))  
    return null;  

  Bookmark sig_bookmark = null;  
  foreach (Bookmark b in richEditControl1.Document.Bookmarks)  
    if (b.Name == "bk_signature")  
    {  
      sig_bookmark = b;  
      break;  
    }  

  DocumentRange rng = null;  

  if (sig_bookmark != null)  
  {  
    // DID find the "bk_signature" bookmark, so just replace...  
    DocumentPosition start = sig_bookmark.Range.Start;  
    richEditControl1.Document.Delete(sig_bookmark.Range);  
    //richEditControl1.Document.RemoveBookmark(sig_bookmark); // <- turns out that we SHOULDN'T delete the bookmark - just the range  
    rng = richEditControl1.Document.InsertRtfText(start, rtfdata);  
    richEditControl1.Document.Bookmarks.Create(rng, "bk_signature");  
  }  
  else  
  {  
    // didn't find the "bk_signature" bookmark, so just insert...  
    rng = richEditControl1.Document.InsertRtfText(richEditControl1.Document.CaretPosition, rtfdata);  
    richEditControl1.Document.Bookmarks.Create(rng, "bk_signature");  
  }  
  return rng;  
}  

Here's the stack trace of the exception being thrown for many (though oddly not all) customers :-

=========================================================
Exception Info: System.Exception
Stack:
   at DevExpress.XtraRichEdit.Model.Paragraph.GetParagraphIndex()
   at DevExpress.XtraRichEdit.Layout.Column.ContainsParagraphFrame(DevExpress.XtraRichEdit.Model.Paragraph)
   at DevExpress.XtraRichEdit.Layout.Column.AddParagraphFrame(DevExpress.XtraRichEdit.Model.Paragraph)
   at DevExpress.XtraRichEdit.Layout.Engine.RowsController.EndRowCore(DevExpress.XtraRichEdit.Model.Paragraph, DevExpress.XtraRichEdit.Layout.Engine.ParagraphBoxFormatter)
   at DevExpress.XtraRichEdit.Layout.Engine.BoxFormatterStateBase.EndRow()
   at DevExpress.XtraRichEdit.Layout.Engine.BoxFormatterStateBase.FinalizeParagraph(DevExpress.XtraRichEdit.Layout.Engine.BoxInfo)
   at DevExpress.XtraRichEdit.Layout.Engine.StateRowEmptyBase.FinishParagraphCore(DevExpress.XtraRichEdit.Layout.Engine.BoxInfo, DevExpress.XtraRichEdit.Layout.Engine.FinalizeHandler)
   at DevExpress.XtraRichEdit.Layout.Engine.StateRowEmptyBase.FinishParagraph()
   at DevExpress.XtraRichEdit.Layout.Engine.StateRowEmptyBase.ContinueFormat()
   at DevExpress.XtraRichEdit.Layout.Engine.StateParagraphStart.ContinueFormat()
   at DevExpress.XtraRichEdit.Layout.Engine.ParagraphBoxFormatter.FormatNextRow()
   at DevExpress.XtraRichEdit.Layout.Engine.ContinueParagraphFormatting.FormatNextRow()
   at DevExpress.XtraRichEdit.Layout.Engine.DocumentFormatter.FormatNextRow()
   at DevExpress.XtraRichEdit.Layout.Engine.BackgroundFormatter.PerformPrimaryLayoutCore()
   at DevExpress.XtraRichEdit.Layout.Engine.BackgroundFormatter.PerformPrimaryLayout()
   at DevExpress.XtraRichEdit.Layout.Engine.BackgroundFormatter.PerformSecondaryLayout()
   at DevExpress.XtraRichEdit.Layout.Engine.BackgroundFormatter.HandleCommand(Int32)
   at DevExpress.XtraRichEdit.Layout.Engine.BackgroundFormatter.HandleCommand(System.WeakReference, Int32)
   at DevExpress.XtraRichEdit.Layout.Engine.BackgroundFormatter.WorkerBody(System.WeakReference)
   at DevExpress.XtraRichEdit.Layout.Engine.BackgroundFormatter.Worker(System.Object)
   at System.Threading.ThreadHelper.ThreadStart_Context(System.Object)
   at System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
   at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
   at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object)
   at System.Threading.ThreadHelper.ThreadStart(System.Object)
=========================================================

Has something been changed internally in the XtraRichEdit control which is causing the above, or is there something wrong with my code?

Many thanks,

Hedley Muscroft