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 south-western Arnhem Land. Our first-hand data reveal 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, summarized by the principle 'mark out the unexpected referent', following McGregor's Expected Actor Principle. 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 an 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.