The other day I was reading my Kindle, having left the WiFi connected in error, and as I turned a page it suddenly locked up. It left me in a bit of a panic as I didn't have any idea what was going on and didn't know if it would recover. Eventually (after about 15 minutes) a message came up to say that it was doing an update.

It would be very nice if they could arrange for it to say what is going to happen, before it happens.

I have mailed Amazon about it and it may have been put on their "lets think about it" list. We will see.

I just posted this so that other users can be aware that their Kindles (mine is a Paperwhite) might do the same when they enable their WiFi.

That's what it does, let it go to sleep with Wi-Fi on and it will check for updates, downloads them and updates itself in a hope it will be finished before you pick it up. So if you don't want this, turn Wi-Fi on only when you really need it and turn it off after.

Yes, I normally run in Aeroplane Mode. I just forgot to go back to that after downloading a book.