Why is this a cross join? - Mailing list pgsql-general

I have a seemingly simple query that returns way too many records.
Here is the count query

select count(*) from (
    select crm.*
    from sap_crm_sales crm
     inner join model_configurations mc on left(crm.customer_class, 6)
= left(mc.sap_code,6)
) as s

The crm table has about 44K records, the model table has about 1K the
join produces about 9 million  records

It doesn't matter if I make it a left join or inner join the count
ends up the same.