Faulty RDF mapping?
I think I found a bug with RDF export: the "Proceedings Title" field of the Conference Paper item type maps to the CSL "container-title" variable (see http://aurimasv.github.io/z2csl/typeMap.xml#map-conferencePaper ; I confirmed that this works correctly in the Reference Test Pane of Zotero 4.0.8). However, upon export to RDF both the "Title" and "Proceedings Title" fields end up in <dc:title/> elements. See https://gist.github.com/rmzelle/5745838
Right now conference proceedings do not have a container (they do have a series). My solution would be to introduce a container of type bib:Proceedings which would serve the same purpose as a bib:Book for bookSection. The title would then go in there.
RDF export really needs to be revisited and revised. There are quite a few problems that I'm seeing.