dupliverting particle systems

I’d really like to have nested particle systems. That is, I’d like for each particle in a particle system effect to be another particle system. I thought one way to do that would be to set up two spheres, each with their own particle system, then use one as a duplivert target for the other.

It works, sorta, in that spheres are emitted by the parent particle system. but the dupliverted spheres do not emit any particles. The real sphere used to generate the virtual copies sits off to the side happily emitting, but the copies don’t. :frowning:

If I go a few frames into the animation and “make dupliverts real”, then the real copies start emitting as they should.

If this is possible, what am I missing?