I am using CC Particle World, and for some reason it seems to put particles that are supposed to be further away in front of particles that are closer to the camera. In the pictured example I used a 'field' of particles with a producer that has a 0px Y-axis to best illustrate what is going on. The particles are all the same size, and therefore the largest ones should be in front of the smaller ones, which is not the case.

I have observed the issue in multiple ways but it's most apparent when the particles are all at the same height.