Does ECID not map automatically to identityMap when uploading data from CSV?
In our sandbox environment I am testing AJO journeys using test profiles created by uploading CSV files with user profile attributes. In the schema used for this, there are fields marked as identities for email address, phone number, loyaltyID, and ECID - all with the correct namespaces. All test profiles are also marked as testProfile = true.

During the data ingestion process I mapped the CSV fields to the appropriate schema fields and created a new dataset. When validating the attributes of the profile that I uploaded using Profiles->Browse I see that all identity fields were automatically assigned to an identityMap namespace except ECID. I attempted to delete and recreate the dataset and the same behavior was observed.
Is the non auto-mapping of ECID a known functionality or is there some step in the process I have missed?