I am not sure that I understand how

copr create different_user/project creates praiskup/project

and

The same thing happens in web-UI, most probably.

This report is related to persistent issue; only admins can toggle
the persistent button when the project is created ... but admins can not
create the project.

ties together. The copr create different_user/project should definitely raise an error that you can't create such project. I am going to fix at least that.

When I'm copr admin, I expect copr create different_user/project to work.

Especially when that is the only way to create project which is "persistent"
(you can not remove builds from it).

I mean copr create some_user/project --persistent.

Modified in PR#1305

Commit be4e9e8 fixes this issue