When a user (not admin) has the privilege of accessing the data source, you can press the button to create a new source or an existing copy.
Both options return "Permission denied!" but the option to copy if you make a copy of the source, which is then the Admin user.
The solution is to disable the buttons to create a new source and copy an existing one.
Yes, the "add" option should not be displayed for non-admin. But the problem with copying (which non-admins can do) is that the user's (cached) permissions were not being refreshed after the copy, so the edit failed. In any case, both issues have been fixed for next release. Thanks for the report.