I used to see this regularly when I was clerk and we had a member receiving counseling that the welfare fund covered. At first, I was unsure so I printed the invoices, had the bishop sign them, and filed with our expenses (this was in the days before EFT reimbursements and all-electronic documentation). Through several audits, the auditors never looked at the documentation and indicated that the fact that they were auto-billed by Family Services was enough for them.
Of course, your mileage may vary, but I stopped printing them and worrying about them - never had an audit flag regarding them.