As I see, your unlink function is not deleting the records. If you decide to override any of the OSV methods, you need to make sure that you call the "super" method prior returning. Here is example:

    def unlink(self, cr, uid, ids, context=None):
        """Remove Ticket Line Record for Account Invoice Line"""
        ticket_line_obj = self.pool.get('ticket.line')
        for id in ids:
            tl_ids = ticket_line_obj.search(cr, uid, [('invoice_line_id', '=', id)], context=context)
            ticket_line_obj.unlink(cr, uid, tl_ids, context=context)                    
        return super(account_invoice_line, self).unlink(cr, uid, ids, context=context)

As you can see, after I have deleted the related objects, I am calling the super.unlink prior returning from the call. This ensures that OSV will delete the record from the database.