The update discussed here ensures that whenever you send an invoice, if the invoice issue date is in the past it will always update to the send date. However this shouldn’t happen if the date is set in the future, as per your original post.
The reason this was implemented is that many users create draft invoices that stay in draft format for perhaps several weeks, when they send that invoice to the client they want the issue date to reflect that (i.e. get updated). When that doesn’t happen if the invoice was created a month ago but sent today, it will instantly show as overdue to the client.