Delphi object reference-counted strings not being released

DelphiBug.dpr

program Project1;

{$appType console}

uses
  FastMM4, SysUtils;

type
  TFoo = object
    s, ss: string; // these fields are released
    constructor Init;
    destructor Done; virtual;
  end;
  PFoo = ^TFoo;

  TDescendant = object(TFoo)
    s2: string; // this field leaks
    s3: string; // this field also leaks
    constructor Init;
    destructor Done; virtual;
  end;
  PDescendant = ^TDescendant;

{ TFoo }

destructor TFoo.Done;
begin
  WriteLn(s);
  WriteLN(ss);
end;

constructor TFoo.Init;
begin
  s := IntToStr(42);
  ss := IntToStr(42);
end;

procedure Lel;
begin
  FastMM4.SetMMLogFileName(PAnsiChar('MM_' + FormatDateTime('yyyy-dd-mm_hh-nn-ss', Now) + '.txt'));
end;

{ TDescendant }

constructor TDescendant.Init;
begin
  inherited Init;
  s2 := IntToStr(43);
  s3 := IntToStr(80085);
end;

destructor TDescendant.Done;
begin
  WriteLN(s2);
  WriteLN(s3);
  inherited Done;
end;

var
  f: PFoo;
begin
  lel;
  ReportMemoryLeaksOnShutdown := True;
  f := New(PDescendant, Init);
  Dispose(f, Done);
end.