ol.mousewheel mxe64

Hi,
I managed to compile an 64-bit externals based on the ol.mousewheel object from Oli Larkin. It works (Max 7 64 bit, Windows 7) but I face an important problem as Max crash when I try to create a second instance... that's annoying, did someone has an idea for that ? (that's my very first externals).

The object need to be started using a 'start' message.

Edit.1 : I also found that, used in a big patch, the 'start' message need to be delayed a bit if loadbang is used.
Edit.2 : And it can also block the scroll inside a patcher windows, it really sucks in fact :D ...help :'(
Here is the source code (also on Pastebin : https://pastebin.com/SqQwG5ST):

/**
    @file
    scrollmouse - send scroll messages to output
 

    @ingroup    examples
*/

#include "ext.h"                            // standard Max include, always required
#include "ext_obex.h"                        // required for new style Max object
#include "jit.common.h"

#include <Windows.h>

////////////////////////// object struct
typedef struct _scrollmouse
{
    t_object                    ob;            // the object itself (must be first)
    void *m_outlet1;
    WNDPROC oldproc;
    HWND hWnd;
    t_symbol *ctxt;
} t_scrollmouse;

///////////////////////// function prototypes
//// standard set
void *scrollmouse_new(t_symbol *s, long argc, t_atom *argv);
void scrollmouse_free(t_scrollmouse *x);
void scrollmouse_assist(t_scrollmouse *x, void *b, long m, long a, char *s);
void scrollmouse_start(t_scrollmouse *x);
LRESULT CALLBACK MyOwnWndProc(HWND hwnd, UINT umsg, WPARAM wParam, LPARAM lParam);

//////////////////////// global class pointer variable
void *scrollmouse_class;

void ext_main(void *r)
{
    t_class *c;

    c = class_new("scrollmouse", (method)scrollmouse_new, (method)scrollmouse_free, (long)sizeof(t_scrollmouse),
                  0L /* leave NULL!! */, A_GIMME, 0);

    // Methods
    class_addmethod(c, (method)scrollmouse_assist, "assist", A_CANT, 0);
    class_addmethod(c, (method)scrollmouse_start, "start", 0);
    class_register(CLASS_BOX, c); /* CLASS_NOBOX */
    scrollmouse_class = c;
}

void scrollmouse_assist(t_scrollmouse *x, void *b, long m, long a, char *s)
{
    if (m == ASSIST_INLET) { // inlet
        sprintf(s, "need a start message %ld", a);
    }
    else {    // outlet
        sprintf(s, "scroll move %ld", a);
    }
}

void scrollmouse_free(t_scrollmouse *x)
{
    ;
}

void *scrollmouse_new(t_symbol *s, long argc, t_atom *argv)
{
    t_scrollmouse *x = NULL;
    long i;

    if ((x = (t_scrollmouse *)object_alloc(scrollmouse_class))) {
 

        x->m_outlet1 = intout((t_object *)x);
 

    }
    return (x);
}

void scrollmouse_start(t_scrollmouse *x)
{
    void *window;

    if(x->oldproc == NULL)
    {
        window = jit_object_findregistered(x->ctxt);
        if(window) 
        {
            jit_object_method(window, gensym("get_window_ptr"), &x->hWnd);
        } else {
            x->hWnd = main_get_client(); //if no argument, get the patcher window 
        }
 

        if(SetProp(x->hWnd,"scrollmouse", x)) {
                x->oldproc = (WNDPROC) SetWindowLongPtr(x->hWnd, GWLP_WNDPROC,(LONG)MyOwnWndProc);
        } else {
            post("Couldn't setProp()");
        }    
    }    
}

LRESULT CALLBACK MyOwnWndProc(HWND hwnd, UINT umsg, WPARAM wParam, LPARAM lParam)
{
    t_scrollmouse *x = (t_scrollmouse*) GetProp(hwnd,"scrollmouse");
    switch (umsg)
    {
        case WM_MOUSEWHEEL:
            //post("a");
            //post("%hd", GET_WHEEL_DELTA_WPARAM(wParam));
            outlet_int(x->m_outlet1, (int) GET_WHEEL_DELTA_WPARAM(wParam));
        return 0; // return, or can also pass to orig proc
    }
    if (x && x->oldproc) return CallWindowProc(x->oldproc, hwnd, umsg, wParam, lParam);
    else return DefMDIChildProc(hwnd, umsg, wParam, lParam);
}