Do you loose power in all gears between 9500 and 12k? Might be worth checking each gear for a similar flat spot, even if you don't have baseline data for each gear. If it's a particular gear, I'd be thinking the trans has something wacked.
Trans slippage can cause power loss in autos, but I don't know M/C trans very well. Does it buck or surge during the flat spot, even slightly?
Just a WAG, but might the KIMS be kicking in from a false (not necessarily faulty, mind you - could be operating out of normal range, but still acceptable; don't know the parms and values involved) TP reading? Likely not, since KIMS doesn't operate at full throttle (assuming the throttle assembly can reach that point, as referenced in the ECU), however it's a thought IF you haven't already disabled it.
Since it's high in the rev range, vibration induced anomalies can occur, like the dreaded grounding problem. If you can monitor your voltage at those rpms, that might help (watch if it fluctuates). Your charging system and battery can also cause all kinds of strange behaviour, so ensuring they're up to snuff - terminals that are corroded and vibrate when loose may cause the injectors and fuel pump to loose some power, not to mention the coil packs.
I've done some work with autos and I've modified my own bikes, but I'm no pro. Just some things to think about. G/L.