хм.. пробвай така:

  TForm1 = class(TForm)

    DBGrid1: TDBGrid;

    Table1: TTable;

    DataSource1: TDataSource;

    procedure FormCreate(Sender: TObject);

    procedure FieldChange(Sender: TField);

  private

    { Private declarations }

  public

    { Public declarations }

  end;





...

var

  Form1: TForm1;

  AlreadyChangedFlag:boolean;

....



procedure TForm1.FormCreate(Sender: TObject);

  var k:integer;

begin

  AlreadyChangedFlag:=false;

  for k:=0 to table1.FieldCount-1

   do table1.Fields[k].OnChange:=FieldChange;

end;



procedure TForm1.FieldChange(Sender: TField);

begin

  if AlreadyChangedFlag then Exit;

  AlreadyChangedFlag:=true;

  try

    if (Sender as TField).DataSet.State in [dsEdit,dsInsert] then

      begin

        (Sender as TField).DataSet.Post;

        (Sender as TField).DataSet.Edit;

      end;

  finally

    AlreadyChangedFlag:=false;

  end;

end;