Juno 60 top octave playing extra notes

[sepulchre]

I’m restoring my old Juno 60 and it has gone well. My repairs have consisted of mainly cleaning the key contacts with contact cleaner, specifically Deoxit. This solved the issues it had before: keys multiple triggering or not at all and retriggering when keys were let up.
The cleaning work fine, but while testing I discovered that the top octave is sort of screwed up. Any note pressed there plays two notes: the note played plus another note that a #5th above it (8 half steps).

More info about this issue: 1 - It doesn’t happen if it’s the arpeggiator playing the notes. ie, play a chord just below the top octave, engage arpeggio and switch it to two octaves. All the notes play fine; no extra notes.

I guess I’ll have to dive in and sus out how notes get triggered from each octave. And then figure out why an extra note is being played 8 half steps above the key pressed in the top octave. If anyone knows how this all works or where I can find such info, I sure would appreciate a pointer.