When filtering issues on the Customer Portal, you are able to filter by who created the ticket, the ticket Status and the ticket Request Type. However this filters will have statuses and request types of all tickets to which a user would have access too - in all projects:

This can cause problems for customers with several projects and request types, as the options on the drop-down menu are limited and one would have to search for the desired request type. Having those tickets filtered by project, before all else, would get the interface to be more friendly for service customers.