I made a post to funny@Lemmy.world, then in another tab I subscribed to science@lemmy.ml. Back in the tab I made the post in, the page updated itself to look like I made the post in science@lemmy.ml instead. I didn’t refresh the page or do anything else… It just changed by itself.
This is likely a websocket issue, in which case, it will be fixed by the release of Lemmy 0.18 (which should be happening in the coming days)