On_change_notify issue

Hi ,

I try to add a simple on_change_notify() to the sale_subscription module. I extend class Subscription with:

 @fields.depends('party')
    def on_change_notify(self):
        notifications = super().on_change_notify()
........
..
            count = Subscription.search_count(domain)
            if count:
                notifications.append((
                    'warning',
                    'Here a wonderful warning'
                ))
        return notifications

The code is working, but the message in Version 8.0 with corresponding Sao client, appears for about 100 milliseconds and disappears again. It just a blink..

Am I missing something?

Thanks for Hints Jakob