Fields are already populated for most recent user

Well I had the same issue today and found that there was a postmeta for the my_account-page containing the value of the field. I had tried to debug this to find out how it can get there but didn’t get very far. Then I just manually deleted the stuff and so far it did not reappear. Maybe not the same as your problem, the value was “sticky” with me (from some customer a while ago) and I hope it still does.

The value should not have been store with the my_account-object of course…