JasonR,

thank you very much for your measurements, but, you know, no good did goes unpunished .
Is there any chance you could run a similar test in stereo mode by applying tone controls? I am curious to see whether the bass rolloff pattern seen in the "bug" matches the crossover and slope of the analog bass tone control.

My thinking is that if it does, then the bug might act totally in the analog domain, and it simply messes up the tone control settings. This doesn't make it any less of a bug, but since you are on this path of tracking it down, this might come across as of interest.

Just a thought...