Sorted! Mark XY Brown 30.Aug.12 10:17 AM a Web browser Domino Designer 6.0.3Windows XP
I sent the template off to a third party Notes developer (Kelros, for those interested), and one of their programmers spotted the problem.
The input translation formula for PeerReviewDetails drives a text value into PeerReviewList. Instead, I amended the formula to use @Name to drive canonical names into PeerReviewList, and this has worked.
(I now feel remarkably daffy for not having spotted that...)