Particle flickering only on render

[animas3D]

Hello,
I set up a particle emitter to emit particles that fade on. When I play the animation in the viewport, it looks good. When I render them out, they are flickery and unusable.
I enabled motion blur on another layer, but not on the layer that has the particles. Maybe I should.
Does anybody have any other idea why this is happening?
Thank you,
Joe.

[Bax Burgess]

Caused by either a multi-thread render of densely bunched particles, or a layer effect in Layer Settings/General.