problems with delphi 4, oracle 8.05 and blobs (wrong size)

I have a big problem to retrieve blobs data from a table in oracle
8.05, with
delphi 4 (update pack 2).

In the database, the blob has a size of 67836 bytes. With the
following code,
i obtain a file of 67837 bytes !!! only one byte, but only one byte
make a tif
file unreadable !

//-----------------------------------------------
procedure TForm1.Button2Click(Sender: TObject);
var
 ablob : tblobstream;
 filestream : tfilestream;
begin
  ablob := tblobstream.create(table1FEU_IMAGE,bmRead);
  if ablob.size = 0 then
  begin
    exit;
  end;
  fileStream := TfileSTream.create('c:\tmp\test.tif', fmCreate or
fmOpenWrite);
  fileStream.copyFrom( ablob, ablob.size);
  fileStream.free;
  ablob.free;
end;
//------------------------------------------------

  I have tried different sizes . here are the result :

  blob size | file size
      2           2        ok !
     2803       2803
     4639       4639
     7405       7405
    10133       10134      BAD !

for all blob sizes > 10134, i obtain one byte more than the blob size