System check Framework error checking Admin Fieldsets in 2.1

[Richard E. Cooke]

This Field set definition:

    fieldsets = (
        ('Job Work Sheet', {
            'fields': (
                    ('number', 'job_history', 'hw_customer',),
                    ('status', 'contracted_out',),
                    ('adn_parts_required', 'atn_required', 'atn_tech', 'cancel_job',),
                    ('date_quoted', 'po_number', 'tag',),
                    ('date_in', 'priority',),
                    ('hw_description', 'hw_make', 'hw_model', 'hw_serial', ),
                    ('technician', 'bin', ),
                    ('assessment_time', 'hours_worked',),
                    ('parts_cost', 'parts_shipping',),
                    ('problem',),
                )
        }),
        ('Hardware Details', {
            'classes': ('grp-collapse grp-closed',),
            'fields': (('hw_customer', 'hardware', ), ('hw_description', 'hw_make', 'hw_model', 'hw_serial',), ('hw_comments',),)
        }),
        ('Repair Details', {
            'fields': (('work_done',), ('comments',),)
        }),
    )

Gets no errors with Django 2.0.6, but with 2.1 I get:

(dj21py37) $ ./manage.py check
SystemCheckError: System check identified some issues:

ERRORS:
<class 'repair.admin.JobAdmin'>: (admin.E012) There are duplicate field(s) in 'fieldsets[1][1]'.
<class 'repair.admin.JobAdmin'>: (admin.E012) There are duplicate field(s) in 'fieldsets[2][1]'.

System check identified 2 issues (0 silenced).



I presume its complaining about the field 'hw_customer', but since it is in readonly_fields this should not be an error, correct?

Rich.