Scott,
I did notice the same thing on my Tyros and my guess was that Yamaha kept the left hand voice off on purpose, to save polyphony.
This is not a big problem for me, because I donīt like the preset OTSs anyway and I always prefer to program my own registrations, but I understand that it can be a frustrating thing.
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Korg Kronos 61 and PA3X-Pro76, Roland G-70, BK7-m and Integra 7, Casio PX-5S, Fender Stratocaster with Fralin pickups, Fender Stratocaster with Kinman pickups, vintage Gibson SG standard.