anchor.diff:  	check_nof_cols(ColsShown, (NofColsShown - NofCols), ColFrameIds, ColIds, 
   		       RowIds, NofRows, RowHeight, FgColor, BgColor ),
   
  -    clear_fields(lists:nthtail(NofColsShown, NewColIds), 
  -		 lists:nthtail(NofRowsShown, NewRowIds)),
  +    clear_fields(safe_nthtail(NofColsShown, NewColIds),
  +		 safe_nthtail(NofRowsShown, NewRowIds)),
   
       RowsToUpdate = lists:sublist(NewRowIds, NofRowsShown),
   
  
positive.code: 
         % Update the ColWidths list.
      TempColWidths = lists:sublist(ColWidths, VirtualCol - 1) ++ 
  	[NewWidthOfCol | lists:nthtail(VirtualCol, ColWidths)],
      
         % Check the other columns, whether a new column has to be created.
      ColsShown    = compute_cols_shown(FirstColShown, TempColWidths, GridWidth, 
  
negative.code:     refresh_visible_rows(RowsToUpdate, NewFirstColShown, NofColsShown, RowDataList, ListAsStr),
  
         % Clear fields currently not visible.
      clear_fields(safe_nthtail(NofColsShown, NewColIds),
  		 safe_nthtail(NofRowsShown, NewRowIds)),
  
      
      NewGridP = GridP#grid_params{nof_cols        = NewNofCols,
  