I'm trying to render out some particles that are being emitted from three fast-moving objects and viewed by a following camera. The particles positions are correct, but when motion blur is turned on the particles get blurred backward and forward from the current frame instead of from the current frame and backward, resulting in renders of particles overshooting their emitters once put into their comp.
Here's a sample render of what the render currently looks like. The streaks forward of the upward swoops shouldn't be there.
Blender Internal's sampled motion blur is better about the forward/backward issue, but the particles are moving so fast that the 32 sample max is insufficient for getting a smooth blur; the samples are far enough apart to be dotted.
So, is it possible for Cycles to sample backward-only motion blur like BI's sampled motion blur does, or is there something else that can be done to achieve the desired effect?
For those interested, here's a link to the Blend file.