It looks similar to problems that arise from off-axis projections, but this projections are straight down the axis. I'm puzzled about what would be causing this, as the same script produced normal, smooth images earlier. Here's the plotting call that I used:
fn = "RD%04i/RedshiftOutput%04i" %(fnum,fnum)
pf = load(fn)
pc = PlotCollection(pf, center=[0.5,0.5,0.5])
for axis in range(3):
p = pc.add_projection("particle_density",axis)