rtx stack overflow due to apparent bug with mailbox implementation

void status_led_task(void const * arg)
{
    bool b_flashing_state = false;

    uint16_t flashing_led_mask = 0;
    uint16_t current_led_mask;
    int current_state;

    osEvent event;
    mail_t * p_mail;

    init();

    while(1)
    {
        /* wait for a message or the desired flashing perid */
        event = osMailGet(g_mail_queue, osWaitForever);//STATUS_LED_FLASHING_PERIOD);

        if (event.status == osEventTimeout)
        {
            /* time to flash any status leds that are in the flashing state */
            if (b_flashing_state == true)
            {
                leds_on(flashing_led_mask);
            }
            else
            {
                leds_off(flashing_led_mask);
            }

            b_flashing_state = !b_flashing_state;
        }
        else if (event.status == osEventMail)
        {
            p_mail = event.value.p;
            current_led_mask = p_mail->led_num + STATUS_LED_GPIO_OFFSET;
            current_led_mask = (1 << current_led_mask);
            current_state = p_mail->state;
            osMailFree(g_mail_queue, p_mail);

            switch(current_state)
            {
                case LED_OFF:
                    /* disable flashing mode for this pin */
                    flashing_led_mask &= ~current_led_mask;
                    led_off(current_led_mask);
                    break;

                case LED_ON:
                    /* disable flashing mode for this pin */
                    flashing_led_mask &= ~current_led_mask;
                    led_on(current_led_mask);
                    break;

                case LED_FLASHING:
                    /* enable flashing mode for this pin */
                    flashing_led_mask |= current_led_mask;
                    break;
            }
        }
    }
}