Usually only one side in a criminal case appeals, but in R v Nguyen  HCA 38 (3 November 2010) the Crown appealed against the Court of Appeal of the Supreme Court of Victoria's quashing of convictions for murder and attempted murder and its entry of acquittals, and the accused (DQN) appealed on the basis of an alleged misdirection by the trial judge by way of failure to leave to the jury the alternative of manslaughter on each count. DQN's appeal point had been raised in the Court of Appeal but was not addressed in its judgment.
The High Court therefore had to consider, on the Crown's appeal, whether the Court of Appeal had been correct in holding that the verdicts had been unreasonable, and on DQN's appeal, whether there had been an error of law.
Both these appeals had to be decided: it would have been insufficient to simply dismiss the Crown's appeal because there had been a substantial miscarriage of justice, because that would leave standing the Court of Appeal's entry of acquittal.
In the result, the Crown was entitled to a retrial because the verdicts were not unreasonable and the Court of Appeal should not have allowed DQN's appeal on that ground. There had to be a retrial because DQN's appeal also had to be allowed: there had been a substantial miscarriage of justice at trial.
Do these two grounds of appeal – reasonableness of verdict, and error of law giving rise to a miscarriage of justice – require different approaches by the appellate court? Both are subject to the proviso that the appeal may be dismissed if no substantial miscarriage of justice had actually occurred.
What is interesting about the High Court's judgment is its absence of reference to Weiss v R (2005) 224 CLR 300. Weiss requires the appellate court, upon finding that there was an error at trial giving rise to a miscarriage of justice, to determine whether the miscarriage was "substantial" by examining the whole of the record to assess whether the prosecution case was proved beyond reasonable doubt. Should you wish, you may locate my earlier comments on this by searching this site on the word Weiss.
In Nguyen the Court applied M v R  HCA 63, (1994)181 CLR 487. This involves asking "was it open to the jury" to convict? It differs from the Weiss question, "is the appellate court satisfied of guilt"?
Plainly, the High Court could not apply Weiss because that would involve saying that it was satisfied of guilt, and also that there had been a substantial miscarriage of justice arising from failure to leave the jury with the alternative of manslaughter. The implications of this appeal highlight how inappropriate the Weiss approach can be.