Great news!

Murray suggested it could simply be that I had a transpose set.. and it was!!

I hardly ever use this feature on any of my synths, but I must have tried it when i was messing around with chord hold.

I’m just amazed that the transpose I had set has survived not only powering on and off multiple times, but a firmware upgrade as well as a factory reset or two. 

Thanks again Murray! - you've just saved me from hours of tortuous double-sided chip removal 

(without a desoldering station - i really must get one of those!).

Waz