Serializer Cache not invalidated correctly when updating linked resource

See components/sib-invoicing#24 (closed)

I POST a CustomerInvoice resource to /customer-invoices/

I then GET /projects/1100/ which the resource is linked to by foreign key, but the invoice is not listed. If I visit /projects/1100/customerInvoices/ then I see the resource listed, which tells me that it's a cache issue