HtoA Alembic instancing motion blur problems

[ola_ph]

I'm having a bit of headache with Arnold, instancing and motion blur at the moment, and hoping maybe someone here have some insight! I've got a little animation cycle of a bird flapping its wings that I'm copying onto some particles using the "copy to points sop". Then I'm doing some offsets and speed variation on the copies by setting the abcframe primitive intrinsic attribute. So far so good; render this with Mantra and motion blur and everything is working as expected. However with Arnold it seems as if the "transforms" are ignored, ie. only the wing flaps are motion blurred, the rest of the bird is razor sharp. Any idea what I'm missing here?

I was able to get it to work in Arnold by reading a bgeo cache of the same anim as a packed disk sequence and manipulating the index intrinsic, but I would prefer to keep things alembic if possible...