Uh oh. Japan's trade and economy ministry is now officially investigating the explosive nature of the iPod nano. The culprit is model MA099J/A -- AKA, the old black and white plastic model already reported to spew "chest high flames," cause bedroom fires, and explode across the floor. The Japan incident occurred in January when an iPod nano reportedly "shot out sparks while recharging." At this point, all odds are with the nano's lithium ion battery. Apple Japan has been ordered to investigate the issue and report back to the ministry with the cause. Kind of like asking the fox what it was doing in the hen house, eh?
Update: Apparently, the Japanese ministry "strongly warned" Apple for failing to report the incident (as required by law) when it occurred. Apple's filing with the ministry came on March 7th.