A paper by Farrell Ackerman, Rob Malouf, and John Moore has just appeared in the Journal of Linguistics! Here’s the abstract.

This paper examines the syntactic and semantic behavior of object arguments in Moro, a Kordofanian language spoken in central Sudan. In particular, we focus on multiple object constructions (ditransitives, applicatives, and causatives) and show that these objects exhibit symmetrical syntactic behavior; e.g., any object can passivize or be realized as an object marker, and all can do so simultaneously. Moreover, we demonstrate that each object can bear any of the non-agentive roles in a verb’s semantic role inventory and that the resulting ambiguities are an entailment of symmetrical object constructions of the type found in Moro. Previous treatments of symmetrical languages have assumed a syntactic asymmetry between multiple objects and have developed theoretical analyses that treat symmetrical behaviors as departures from an asymmetrical basic organization of clausal syntax. We take a different approach: we develop a Head-Driven Phrase Structure Grammar account that allows a partial ordering of the argument structure (arg-st) list. The guiding idea is that languages differ with respect to the organization of their arg-st lists and their consequences for grammatical function realization: there is no privileged encoding, but there is large variation within the parameters defined by arg-st organization. This accounts directly for the symmetrical behaviors of multiple objects. We also show how this approach can be extended to account for certain asymmetrical behaviors in Moro.