saveas_dialog crashes max

hi there,
what i eventually want to come up with, is a dialog that lets the user select a folder (like [savedialog fold] in max).
so i'm experimenting with saveas_dialog() and saveasdialog_extended() - both seem to have severe problems (or maybe it's just me?) - Max 6.1.6 & SDK 6.1.4 on mac os 10.6

in the stripped down example below both calls to saveas_dialog or saveasdialog_extended crash badly - even without the time for a crash report or anything - where as the call to open_dialog() works fine.

something similar appeared here https://cycling74.com/forums/alternative-to-saveasdialog_extendedfilename-path-outtype-filetype-1/
but unfortunately didn't lead anywhere.

does anybody see what's wrong?
thanks,
volker.

#include "ext.h"
#include "ext_obex.h"
#include "ext_common.h"


static t_class *myObj_class;
typedef struct {
    t_object b_ob;
} t_myObj;


void *myObj_new( t_symbol *s, long argc, t_atom *argv);
void myObj_saveme(t_myObj *x);
void myObj_dosave(t_myObj *x);


int C74_EXPORT main(void) {
    t_class *c = class_new("testSaveas", (method)myObj_new, 0, (short)sizeof(t_myObj), 0L, A_GIMME, 0L);    
    class_addmethod(c, (method)myObj_saveme, "bang", 0);
    class_register(CLASS_BOX, c);
    myObj_class = c;
    return 0;
}


void myObj_saveme(t_myObj *x) {
    defer_low(x, (method)myObj_dosave, 0, 0, 0L);
}


void myObj_dosave(t_myObj *x) {
    short        pathID;
    char        filename[MAX_FILENAME_CHARS];    
    t_fourcc    type;
    

    // open_dialog(filename, &pathID, &type, 0L, 0);        // works fine
    saveas_dialog(filename, &pathID, NULL);                //