Admin cannot change role of another existing user to admin

[anon77445132]

To Reproduce
Steps to reproduce the behavior:

1. I have installed a fresh Kirby 3.3.2 Starterkit (on Win10: XAMPP 7.3.12 – Apache/2.4.41 (Win64) OpenSSL/1.1.1c PHP/7.3.12).
2. I have added user blueprints for the roles “admin” (only fields), “editor” and “visitor”.
3. I’m logged in as user#1 as admin.
4. I create a new user “editor” with the role “editor”.
5. I create a new user “visitor” with the role “visitor”.
6. After that (may be some months later) I want to change the role of the user “editor” to the role “admin”:

Describe the bug
I cannot find this role (look at the hardcopy). It is missing in this Kirby version.

Expected behavior
It is correct, that only someone with the role “admin” should be able to do this.
But he/she should be able to do this using the panel I think.

Kirby Version
Tested with Starterkit 3.3.2

[Added:]
While there are at least TWO users with the role “admin”, then as admin I can change the role of an existing user to “admin”.
If later there is only one admin, the issue is back.