Attachments on emailed invoices - Bulk sent

Could you please allow the function of attachments being attached to invoices that are bulk/batch emailed?  Attachments are sent when emailing one invoice at a time, but they aren't attached when you are sending multiple emails at a time.  I am unsure why attachments are enabled if they can't be sent every time regardless of whether you send an invoice individually or multiple invoices at the same time.