NDS Development: Don't always trust the tools...
Fun fact: sometimes when you try to compile your code, the devkitPro compiler will not be happy and have compiler errors, but still reports back a successful compilation. Generally that's not a problem so long as you're not relying on the bottom message to decide if your code worked or not, but if you're developing in, say, Visual Studio, and your IDE is just reading the last bit to decide if stuff worked, and you always launch into the emulator right after building, you'll just keep seeing an old version that isn't new and your bugs won't go away and you'll spend a lot of time working out things you've actually already fixed...
TL;DR, just read the output logs when you have bugs - it could save your life. :D
Also: DeSmuME does not properly emulate the fact that the background scroll registers are write-only (ie, you can't use += with them and expect that to work on hardware, but it will be fine on the emulator). Why are they write-only? *shrug* But you need to know that if you want your background to not be static (which you probably will).