I just went through this problem again with a new SL88 Studio that I bought. I also have a SL88 Grand, so that's why I say "again".
I thought I'd put it out here since I couldn't find the issue discussed anywhere and will show the fix.
The problem is that the damper pedal changes programs as well as sustains the keys played.
I think it's the firmware update v1.6 that causes the issue, but not sure. I didn't see anywhere in the SL Editor that would affect it.
The way to fix it is in the Global Settings, the default setting for "Programs +/-" is 999. Change it to OFF. Again, I think the firmware v1.6 did this, because before I installed it, the damper pedal didn't do this.
Have a nice day!