There are some defense lawyers - you know who they are - who resist ever writing a motion or a demurrer or a special jury instruction. They have their rationalizations, and I won't soap-box about it now. But there are times their aversion to paperwork might be fatal to their client's appeal in a way they might not have considered.
And that is when the lawyer, in a co-defendant case, says to the court, "I'll join in the co-defendant's [special jury instruction/demurrer]," in lieu of filing a motion of their own.
While this may not be bad practice every time, both demurrers and special jury instructions are required to be in writing and filed with the court.
A Proposed instructions. Unless otherwise requested by the trial judge on timely notice to counsel, proposed instructions shall be submitted at the commencement of the trial. Proposed instructions upon questions of law developed by the evidence, which could not be reasonably anticipated, may be submitted at any time before the court has instructed the jury. The number of copies of proposed instructions and their form shall be governed by local court rule."
ORS 135.610 (2) The demurrer shall be in writing, signed by the defendant or the attorney of the defendant and filed. It shall distinctly specify the ground of objection to the accusatory instrument.
Co-defendants may be on the same indictment, but they have different case numbers. This means there are different court files for each co-defendant. So whatever jury instructions the attorney "joins" in, those instructions could only be found in the other defendant's file. Even if there weren't separate court files, the "joining" co-defendant hasn't submitted a demurrer in writing, much less signed it.
Have I ever seen an appellate court reject an argument as unpreserved in this situation? I haven't, but that hardly means it hasn't occurred, and let's face it, my clients won't be in that situation. Even if it wasn't fatal, it would still mean more work for the appellate attorney, and it risks a fight over preservation, which can use up all the oxygen that otherwise would have been spent arguing the merits.
And if nothing else, it makes one of the lawyers look less prepared than the other.