Yeah this happened at the Off-road Nats this year. Someone finished charging a pack and put it back in his battery box, a couple of minutes later it started smoking and then at least one cell blew.

Here are some pics:
http://www.rcracephotos.com/displayi...album=7&pos=44
http://www.rcracephotos.com/displayi...album=7&pos=46
http://www.rcracephotos.com/displayi...album=7&pos=42

As for putting them in a box, you can do it, but I think its just one of those rare things that happens. I won't be changing my charging habits because of it.