To be fair, you get a message at the start warning you to lock in ban picks and champ picks. -- a warning that comes up every time you start a queue unless you switch it off. You only forget if you're not paying any attention to the game lobby.
It's pretty forgivable atm not only because people are so used to it just locking whatever you have selected when your timer runs out but also because you can't actually look at your champs before you pick, which is pretty important when you're trying to pick for your comp/counter pick. That should be fixed next patch I believe and hopefully people can get used to locking in and it won't be a problem