Why Does Describe Information Always Return True for Updateable on Read-Only Fields?

Question

I cloned the Administrator profile, removed the Edit permission for some fields on Opportunity Product, and applied the cloned profile to a non-admin user. I logged in as this user and went to a Lightning page that runs backend code that checks permissions using describe information for opportunity product. For some reason, the field that I removed the "Edit" permission from is "Updateable" according to the describe information. Only by removing the "Read" permission for the field as well that "Updateable" returns false, but I want the field to be readable and not editable.

Answer 1

The administrator profile have permission Edit Read Only Fields provided in System permissions for the profile. This might have got copied over.