Acually, it's how the DS is built. You have a maximum of 4 layers on each screen due to the way VRAM is designed and you can do nothing about it unless you somehow write your own library to control the priorities.
In any case, you can select Layers using Advanced Change Background.
FalloutDS: Postponed until proper libraries are created, 10%
Foxi_Lib: A completely revised version of NitroSprites[FINAL], NitroBackgrounds and NitroText[FINAL], 40%