adding user with already existing login and changing his privileges occurs with error

While adding a new user (privileges = user) with a login that already exists piotr.gawron, I got correct warning that user already exists. Then, I modified the login for unique one piotr.gaw, and I changed the privilege on admin. After that I got error invalid role: undefined. I closed the error dialog and clicked SAVE. The user piotr.gaw was added with privileges user. See images below.

NOTE: If I was logged as ewa.smula and tried to add ewa.smula with user privilege -> got the warning that user exists already -> changed login to ewa.smul and admin privileges -> I got the error dialog invalid role: undefined and the ADD USER window got closed on its own.