The mode for creating documents from orders on the issued invoices side — the taxable supply date (TSD) is, according to the VAT Act, the date the delivery is fulfilled or the date of payment, whichever occurs first.
For this reason, on the issued invoices side, the date from the warehouse goods issue note is automatically pulled into the TSD field. In conjunction with inventory management, the TSD, quantity, and selling price (not the stock price, which is subject to automatic calculation) are carried over to the invoice.
The situation is different for received invoices — here you are required, when recording an invoice, to use the dates stated on the invoice itself. There is no legal requirement that a warehouse goods receipt must be created with the taxable supply date — in fact, it is not even possible to know in advance what TSD will appear on a future invoice.
It is entirely common, for example, for goods to be received repeatedly on different days — meaning multiple warehouse receipts are created, while the recipient receives only a single invoice summarizing all billed deliveries and, naturally, containing only one TSD. It also frequently happens that, for instance, a delivery note does not include prices, or the price on the invoice has been reduced by a discount.
The software cannot predict these circumstances in advance, just as it cannot predict what TSD will appear on a received invoice. This is why, when pulling in warehouse receipts, the method chosen is to transfer the date from the receipt to the TSD of the received invoice. It is primarily for these reasons that the purchase side does not work in the same mode as the sales side.