The Camera IMBlur operator corrects a problem in which Image Motion Blur applied to a Particle Flow system might not render properly when the camera is animated. The operator adjusts the particle speed, accounting for camera motion, before it's passed to the viewport display and/or the renderer. Internally, the Particle Flow engine continues to use the true particle speed for the animation.
Add the Camera IMBlur operator to any event to which you've applied Image Motion Blur. Alternatively, to apply Image Motion Blur to the entire animation, add the Camera IMBlur operator to the global event (by default, PF Source 01), and turn on Image Motion Blur for the global event (via Properties) as well.
Alternatively, you can exaggerate the camera motion by setting up a specific Multiplier value in the interface. Default=on.