Consistent with military law, the federal circuits generally follow the principle that evidentiary errors in a judge alone case are often nonprejudicial. The basic theory being that judges are presumed to know and apply the law, and will ignore impermissible evidence even where there has been no objection.
The Seventh Circuit recently considered the different treatment in admitting evidence in a bench trial instead of a jury trial; the circuit applies a “presumption of conscientiousness” in reviewing evidence admitted in a bench trial; while any error was ultimately harmless, the circuit notes that “had the evidence come before a jury, we may have come to a different conclusion, but we presume that the court was not unduly influenced by this weak pattern evidence,” in United States v. Reed, _ F.3d _ (7th Cir. March 10, 2014) (No. 12–3701).
On a side note to this case, another caution regarding “talismanic incantations” of admissibility of other acts evidence.