No I don't think it is just inherent in the camera. The blue led has a fairly narrow spectrum (say 25nm at most) so producing a 150nm 'spread' would mean a broad angle of light impinging on the DVD -- which doesn't appear to be right.
As I recall, some user-posted CFL spectra show this effect and some do not. My early experiments with the old camera did have some noise but not this much in the blue. I think a common problem is having the CFL source much too close to the spectrometer (so having the inverse of a 'point source') which easily causes additional internal reflections along with other issues.
Having a large, broadband 'false signal' included does a lot of damage to the data from the true signal. When the true signal is 20dB below the noise, even complex correlation techniques cannot extract the signal data so it is not just a simple subtraction to look for the difference. Noise is always a killer of signal data and, generally, signals need to be at least 6dB above the noise to be 'usable'.
To get a visual sense of the error, just compare the original CFL spectra I collected using the original PLab 'box' camera with my latest Hi-Rez configuration. The difference is dramatic -- and the plots were extracted from the same CFL (and none of them have 'broadband blue noise'.
It would be good to track-down the root-cause of the blue error. Try this: 1) a darkened room, 2) CFL at a distance of 3-5 feet, 3) could also block all light from CFL except for a 1-inch hole in a cardboard mask to further restrict the source angle, 4) DVD parallel to camera sensor, mounted very close to the lens, 5) DVD at 45-deg to direction of slit, 6) slit at least 8-10 inches from camera, 7) mechanically stable (sitting on the desk) then 8) focus for best resolution of mid-green double-peak. Under these conditions, I often just use a black cloth to cover the spectrometer parts which usually eliminates nearly all stray light.