(curious) What if a user closes it before 4 seconds? Ctrl+enter, it optimistically locally updates within 1 second. I close ctrl+w. But my wifi goofed and it didn't reach the server.
The HTTP request is fired off instantly, so chances are that the request is already written to the socket and closing the page won't cancel the request. Should your wifi-router drop it, your client will retain the transaction on disk and retry it the next time you come online.
I have mysteriously lost comments/descriptions I wrote on issues. I figured it was related to a failed and lost opportunistic update like this, although I suppose it could have been caused by a fixable bug.