Memory leak using IHTMLEventObj handlers with TWebBrowser

I'm using a TWebBrowser to display a WYSIWYG HTML editor and I've added some handlers to catch keyboard and mouse events so I can integrate this editor into my application flow. This browser is integrated in a custom TPanel, TPanelEditorHTML.

This is the way I'm doing it, following some tips from this answer:

  //Create the procedure type to assign the event
  THTMLProcEvent = procedure(Sender: TObject; Event: IHTMLEventObj) of object;

  //Create a  new class for manage the event from the twebbrowser
  THTMLBrowserEventLink = class(TInterfacedObject, IDispatch)
  private
    FOnEvent: THTMLProcEvent;
  private
    constructor Create(Handler: THTMLProcEvent);
    function GetTypeInfoCount(out Count: Integer): HResult; stdcall;
    function GetTypeInfo(Index, LocaleID: Integer; out TypeInfo): HResult; stdcall;
    function GetIDsOfNames(const IID: TGUID; Names: Pointer;
      NameCount, LocaleID: Integer; DispIDs: Pointer): HResult; stdcall;
    function Invoke(DispID: Integer; const IID: TGUID; LocaleID: Integer;
      Flags: Word; var Params; VarResult, ExcepInfo, ArgErr: Pointer): HResult; stdcall;
  public
    property OnEvent: THTMLProcEvent read FOnEvent write FOnEvent;
  end;

On my container for the TWebBrowser I have this:

FOnKeyDownConnector:  IDispatch; 
FOnClickConnector:  IDispatch;
FOnKeyDownConnectorIFrame:  IDispatch;
FOnClickConnectorIFrame:  IDispatch;    

procedure BrowserIHTMLDocument2OnKeyDown(Sender: TObject; Event: IHTMLEventObj);
procedure BrowserIHTMLDocument2OnClick(Sender: TObject; Event: IHTMLEventObj); 
procedure IframeIHTMLDocument2OnKeyDown(Sender: TObject; Event: IHTMLEventObj);
procedure IframeIHTMLDocument2OnClick(Sender: TObject; Event: IHTMLEventObj);

Where BrowserIHTMLDocument2OnKeyDown, etc are the procedures where I do all the work integrating the HTML editor data into my application

I create the handlers on startup

constructor TPanelEditorHTML.Create(AOwner: TComponent);
begin
  inherited;
  // ...
  FNavegador := TGENBrowser.Create(self);
  FOnKeyDownConnector := THTMLBrowserEventLink.Create(BrowserIHTMLDocument2OnKeyDown);
  FOnClickConnector := THTMLBrowserEventLink.Create(BrowserIHTMLDocument2OnClick);
  FOnKeyDownConnectorIFrame := THTMLBrowserEventLink.Create(IFrameIHTMLDocument2OnKeyDown);
  FOnClickConnectorIFrame := THTMLBrowserEventLink.Create(IFrameIHTMLDocument2OnClick);
end;    

And when I load the HTML editor I assign this handlers to a couple of elements in the DOM tree:

procedure TPanelEditorHTML.AsignarManejadores;
var
  HTMLDocument2_A, HTMLDocument2_B: IHTMLDocument2;
begin
  HTMLDocument2_A := ExtraerIframeEditor;
  HTMLDocument2_B := (FNavegador.Document AS IHTMLDocument2);
  if (HTMLDocument2_A = nil) or (HTMLDocument2_B = nil) then
    Exit;

  if (FOnKeyDownConnectorIFrame <> nil) then
    HTMLDocument2_A.onkeydown := FOnKeyDownConnectorIFrame; 
  if (FOnClickConnectorIFrame <> nil) then
    HTMLDocument2_A.onclick := FOnClickConnectorIFrame; 

  if (FOnKeyDownConnector <> nil) then
    HTMLDocument2_B.onkeydown := FOnKeyDownConnector; 
  if (FOnClickConnector <> nil) then
    HTMLDocument2_B.onclick := FOnClickConnector;   
end;

When the user ends the editing I remove this handlers

procedure TPanelEditorHTML.DesconectarManejadores;
var
  HTMLDocument2      : IHTMLDocument2;
begin
  HTMLDocument2 := ExtraerIframeEditor;
  if (HTMLDocument2 <> nil) then
  begin
    HTMLDocument2.onkeydown := Unassigned; //assign the event handler
    HTMLDocument2.onclick := Unassigned; //assign the event handler
  end;

  HTMLDocument2:=(FNavegador.Document AS IHTMLDocument2);
  if (HTMLDocument2 <> nil) then
  begin
    HTMLDocument2.onkeydown := Unassigned; //assign the event handler
    HTMLDocument2.onclick := Unassigned; //assign the event handler
  end;
end;

My problem is on the TPanelEditorHTML destructor. This leads to a memory leak of the four THTMLBrowserEventLink. If I try to FreeAndNil the handlers I get a runtime error.

destructor TPanelEditorHTML.Destroy;
begin
  FDataLink.Free;
  FOnKeyDownConnector := Unassigned;
  FOnClickConnector := Unassigned;
  FOnKeyDownConnectorIFrame := Unassigned;
  FOnClickConnectorIFrame := Unassigned;
  inherited;
end;

I found this article about memory leaks and I tried to replace both methods that were making copies to no avail.

Am I missing something?

As @DalijaPrasnikar said there is a superfluous _AddRef in THTMLEventLink.Create, wich I copied from the solution proposed in this answer.

Changing the constructor of THTMLBrowserEventLink to this:

constructor THTMLBrowserEventLink.Create(Handler: THTMLProcEvent);
begin
  inherited Create;
  FOnEvent := Handler;
end;

Avoids the memory leak.