Material interpolation/DR problem?

Finally getting back to finishing a test file and was running a hi-res render tonight and got this odd result:

I have never had “lost” buckets render with depth of field before - very odd. This file rendered fine in lo-res, and I ran crops of the hi-res without issue. It’s not a usual DR thing ( I’m using UNC paths etc, and everything has been fine till now).

The material here is using reflect/refract interpolation, and I know there have been problems with that in the past, and wondered if that was the culprit here. I thought SP3 fixed that problem though - is there still a known issue with that? Any other ideas what would cause this?

Thanks for any help.
b

The buckets appear to be on the SSS2 material and not related to DOF (although material inteprolation may have something do to with it); I’ll have to check.

Best regards,
Vlado

This image is not using SSS2, just regular Vray mats with interpolation in both reflection and refraction. I switched to trying the SSS2 after this problem cropped up.

b