I remember when that happened to me the first time. I knew from a friend that it changed tone on your birthday but I forgot all about it. Turned on my DS on my birthday and thought something was broken lol
The first time I got this on my DS Phat I did not know about it and at first I also thought something was broken, until my still sleepy mind put 1 and 1 together. And I already had the system for 2 years or so, I just never used it on my birthday before.