idx := -1;  //  this is the start

  if fSorted then  //  is false for sequences i.e. nested DICOM groups
  ...

  if idx > -1 then  //  we won't go in here because idx is still -1
  begin
  ...
  else
  begin
    // append to the end
    idx := fTags.Add(tag);  //  we'll hit this code, so idx will be > 0, as the same tag already exists
  end;


  //  at this point, we have at least 2 identical tags, the old one and the new one.  
  if ReplaceIfExist then
  begin
    // remove possible other replications
    i := 0;
    while i < fTags.Count do
    begin
      if (PIEDicomTag(fTags[i])^.Group = Tag^.Group) and (PIEDicomTag(fTags[i])^.Element = Tag^.Element) and (i <> idx) then
        DeleteTag(i)  //  the old tag will be deleted, which is correct, but because i is not incremented, the new tag will also be deleted as i <> idx (of the new tag)
      else
        inc(i);
    end;
  end;