This article discusses the distribution and function of a suffix that has been labelled "ergative" in the literature on Dalabon, a Gunwinyguan (non-Pama-Nyungan) language of southwestern Arnhem Land. Our first-hand data reveals that although this marker (-yih) more frequently occurs on A arguments of multivalent clauses, it also appears with significant frequency on S arguments of monovalent clauses, particularly with the verb root yin 'to say, to think, to do'. We explain this non-canonical distribution with a co-dependent analysis of its discourse and pragmatic functions, summarised by the principle "mark out the unexpected referent", following McGregor's Expected Actor Principle (1998:516). These functions differ slightly according to clause type. For both types, the marker has a discourse function of "mark out the non-topical referent": either an A argument that sufficiently threatens the construal of local topics, or a S referent after a long period of deferred topichood (particularly speaker referents). The marker also has a correlating pragmatic function of "mark out the contrary referent": either an A participant acting against the motivations and expectations of other (topical) referents (or of the speaker), or an S participant with an unusual stance or speech content.