In Particles Settings, where you specify the material index to use, there is a limit of 16. Is this just something that was overlooked from 2.49?
Time was that Blender could only have 16 materials on an object, but that has changed in 2.5. Shouldn’t the Particles Settings be able to address the additional materials?
I’ll submit a bug report if no one can think of a reason to limit the max material index to 16.