I should point out that even with the 'correct' setting (which isn't default) whatsapp will still re-encrypt and re-transmit any unsent messages under the new k

I should point out that even with the 'correct' setting (which isn't default) whatsapp will still re-encrypt and re-transmit any unsent messages under the new key. All the 'correct' setting does is notify you of the key change. The article is factually wrong on this.