I have checked your issue at my end with Gtk and web-client both But all are working as expected.
I have put a constraint in res.partner object which you have gives in bug specification and try to create a new partner with same reference but the constraint call successfully and I am not able to faced any traceback.
I have attached a video for your more reference so would you please check it and notify us where you faced the problem.
Hello Manfred,
I have checked your issue at my end with Gtk and web-client both But all are working as expected.
I have put a constraint in res.partner object which you have gives in bug specification and try to create a new partner with same reference but the constraint call successfully and I am not able to faced any traceback.
I have attached a video for your more reference so would you please check it and notify us where you faced the problem.
Thanks and waiting for your reply!