Another reminder to myself (like nearly all the posts in this small diary) to rely whenever possible on the Content Query WebPart “PageFieldValue” for the relation between content.
No custom user/web controls wrapped or not in webpart(s), no extensive search service configuration and core search result webpart configuration (altough I still like that option !), the good old trusty CQWP with its PageFieldValue and the ability to work natively with Managed metada field (including children terms) is a pure joy to use.