Invoice date of shipment product

Hello fellow friends,

when using the invoice grouping module, invoice lines sometimes appear in more or less random order. To achieve a nicely sorted customers’ invoice, where every shipment is grouped in a certain block with a headline, we (with help of my valued friend @mstma ) are trying to develop a module.

Now we find that sales date of the carrier products always is set to “today’s date”. Is this intended behavior? - For our purpose (and IMHO in general) we tend to the opinion that it would make more sense to attribute the actual shipment date, meaning the “effective date” assigned at the shipment process.

Or is there a good reason for using “today’s date”?