Perhaps you can understand Keychat's continual updating of sending addresses as akin to Signal's sealed sender feature.
“When you send a traditional piece of physical mail, the outside of the package typically includes the address of both the sender and the recipient. The same basic components are present in a Signal message. The service can’t “see into” the encrypted package contents, but it uses the information written on the outside of the package to facilitate asynchronous message delivery between users.
While the service always needs to know where a message should be delivered, ideally it shouldn’t need to know who the sender is. It would be better if the service could handle packages where only the destination is written on the outside, with a blank space where the “from” address used to be.”