For me, it's a little hard to see what harm was done by the extra instructions to the jury. I would be inclined to side with the two appellate court judges who dissented from the majority opinion. The two of them said that the additional instructions that the judge gave were irrelevant, but that this was a "harmless error."
The majority opinion held that these extra instructions could be so distracting to the jury that it might impair the defendant's ability to have them focus on the case at hand. I find it hard to believe that this distraction would constitute such a huge problem as to overturn a verdict.
However, it is probably true that judges should not let juries get distracted by points of law that aren't relevant to the case at hand. Perhaps it was appropriate for the appellate court to use this case to send a message to trial judges.
Without being privy to all of the information and evidence presented in the case, it's hard to assess the court's ruling without being completely subjective. It basically comes down to whether or not I agree with the legal principle defined by the appeals court in the ruling.
My answer to that is yes. While I support the discretion of judges in criminal court trials remaining intact, I tend to lean towards the use of that discretion in sentencing more so than in the conduct of the trials, and especially as they regard to jury deliberations.
The introduction of new information by the judge in the original trial could easily have swayed members of that jury towards conviction, and in essence extended the trial after the proceedings had finished by adding the burden of proof to the defendant after the closing arguments had been made. On the surface anyway, it seems like the judge pretty clearly stepped over the line.