you mean its not every 6 one in a row , like in half steps , but , what ever the 6th key you press is in any intervals?

it has 6 voices and it rotates witch voice sounds, so the chip for your 6th voice might be dead.
test it out play any 5 notes not octaves over and over no problem then add a 6th note and see what happens. then try playing the 6th note octaves of the other notes your playing they might sound. anything else probly wont then.

so that would make it mint for 5 note bass lines?!?