Accessing nickname of linked Facebook account not possible?

When I create a new auth0 account with Facebook as the primary auth source, I am always able to access the .nickname property (from the result of getUser())

On the other hand, if I create a new auth0 account with Twitter or Google as the primary auth source, and link a Facebook account to it, then nickname is not in the profile data for the linked Facebook identity

Is this by-design, and if not, how do I access the nickname of Facebook accounts that are linked but not the primary auth source?