The end of cell mark is being treated as a return character when applied to the target BM. You will need to clip the range of the source text. Assume I have a table cell bookmarked "A" and want to copy duplicate the text at bookmark "B"

Sub ScratchMacro()
'A basic Word macro coded by Greg Maxey
Dim oRng As Word.Range
Dim oRngSource As Word.Range
  Set oRng = ActiveDocument.Bookmarks("B").Range
  Set oRngSource = ActiveDocument.Bookmarks("A").Range
  oRngSource.End = oRngSource.End - 1
  oRng.Text = oRngSource.Text
  ActiveDocument.Bookmarks.Add "B", oRng
lbl_Exit:
  Exit Sub
End Sub