Titan_M2 Yes, that's how it works: https://signal.org/blog/there-is-no-whatsapp-backdoor/
Okay. That explains my observation totally. It is just I didn't expect they would ask senders to resend already sent but not yet delivered messages under new keys. Strictly speaking, that means some sensitive messages and media might get exposed, without the sender knowing beforehand, just after the fact, so seems like a very bad design choice. But since it is the design choice they have made, messages are still technically end-to-end encrypted between sender and recipient, just some might get exposed.