Several things could have happened:
My guess would be that someone was pressing the sustain pedal the last time it was played or unplugged. To correct the problem, I would try plugging in a pedal before turning it on next time, and then pressing the pedal after it's powered up. Just a guess.
On the other hand, someone could have assigned CC64 to the mod wheel or to the data entry sliders. Try moving each to see if affects the sustain.
Or they might have done either of the above for the default performance. Try changing performances to see if other performances have a pedal-up sound. If so, you can go back to the default performance and edit it so that pedal-up is the default setting. Or they might have assigned the Organ Combination with a strange envelope. See page 16 of the manual for Performance Parameters: http://download.yamaha.com/api/asset/file/?language=hu&site=hu.yamaha.com&asset_id=7058
Or it could be booting up in Dual mode, with both a piano and, say, strings loaded, so that after a note is released, the longer decay of the strings is heard.
It's less likely, but possible, that someone could have used software and made pedal-down the default sound, or increased the release portion of the envelope.