[berkut]

Looking at the diff they did it doesn't really look that way (only had a quick glance though).

Looks like they're not using a swept BVH (interpolated time segments) for motion blur which seems weird, instead leaf nodes seem to be duplicated for each time sample.

So it looks like they're just making savings by skipping motion segments outside the current ray time, and I'd assume the bboxes of the parent inner nodes are all much bigger than they need to be (as they're not swept), and so intersection performance is still quite bad (compared with how it could be)?