Nicely argued. I was preparing to further argue the point when I saw that the two protagonists debating the point were Australian, but had to revise my stance once I saw the OED reference. Given that reference, I'm prepared to amend my observation to "they're both idiomatically correct", though...
Hmm. Replace "wrong" with the synonym "incorrect". That illustrates that the adverb is the better option, notwithstanding the fact that the meaning of the sentence containing the adjective is clear.