MtoA Motion Vectors in Nuke for Instanced Particles

[Will_Atkin]

Hi Everyone.. I'm having vectorBlur problems in Nuke when I render instanced particles. The particles themselves are simple cylinders with linear transformations (think bullets), I'm rendering in Arnold 5 using nuke vectorBlur2.

I have already found the AOV shuffle fix (motion vector AOV needs to be in nuke motion layer).. and confirmed this worked with a test scene using a transforming primitive, but my particles are still not blurring correctly.

If the particles have a horizontal transformation from right to left, the vectorblur shows a diagonal blur:

As I've already confirmed the vectorBlur2 node functions correctly, I think the motionvector AOV is not being written correctly for the particles. Any advice?

Thanks in advance!