I have some problems with com interfaces (refcounted): in this simple program heaptrc reports a memory leak even if the destructor was correctly called:

{$mode objfpc}{$H+}
{$interfaces com}
program moneyleak;
type
  IMoney = interface
  ['{AAD734A1-6F35-D911-9C73-C6AC7996EDD0}']
  function Add(aMoney: IMoney): IMoney;
  end;
  TMoney = class(TInterfacedObject, IMoney)
  private
    FAmount: Int64;
    FCurrencyUnit: string;
  public
    function Add(aMoney: IMoney): IMoney;
    constructor Create(aAmount: int64; aCurrencyUnit: string);
    destructor Destroy; override;
  end;
  function TMoney.Add(aMoney: IMoney): IMoney;
  begin
    Result := nil;
  end;
  constructor TMoney.Create(aAmount: int64; aCurrencyUnit: string);
  begin
    Inherited Create;
    FAmount := aAmount;
    FCurrencyUnit := aCurrencyUnit;
  end;
  destructor TMoney.Destroy;
  begin
    FCurrencyUnit := '';
    writeln('Destroyed');
    inherited Destroy;
  end;
procedure TestLeak;
var
  a: IMoney;
begin
  a := TMoney.Create(12, 'EUR');
end;
begin
  TestLeak;
end.

The compilation and the results:

demo]$ fpc -gh -gl moneyleak.pp
Free Pascal Compiler version 1.9.5 [2004/10/24] for i386 Copyright (c) 1993-2004 by Florian Klaempfl
Target OS: Linux for i386
Compiling moneyleak.pp
Linking moneyleak
50 Lines compiled, 0.1 sec
demo]$ ./moneyleak
Destroyed
Heap dump by heaptrc unit
1 memory blocks allocated : 32/32
0 memory blocks freed : 0/0
1 unfreed memory blocks : 32
True heap size : 557056 (16 used in System startup) True free heap : 556944
Should be : 556952
Call trace for block $4000004C size 32
$08052F26
$08053922
$0805C456 TMONEY__CREATE, line 28 of moneyleak.pp $0805C60C TESTLEAK, line 45 of moneyleak.pp

What am I doing wrong?
Thank you in advance for any help,

Regards,
Dean Zobec