I too have a KX-88 that I love, but it bit the dust recently. It is stuck in dual mode and therefore spits out two midi notes simultaneously into my midi tracks in DP.
I have go to each note and click on each note and hit delete. Way too time consuming.
I opened the keyboard and unplugged every multi-pin connector and reconnected them and that fixed the problem. Then a few weeks later, it acted up again, so I did the same thing again only this time it did not fix it.