Hierarchical Select field as required field on user profile with Custom Field Permissions

Here is the scenario:

• I created a field Categories on users profile with widget type as HS
• This field is required but it can only be edited by a specific role e.g. 'Teacher'
• To do this, I used Custom permissions on field configuration form where only "Teacher" role is allowed to Edit and create value for this field.
• But when I save the profile of normal authenticated user, is says "Categories field is required" but only users with role 'Teacher' can edit this field

Is there any work around for this kind of a situation? I want to permit every 'Teacher' to edit the categories field but cannot allow normal users to edit/view this field