If you press the sustain pedal and it turns off the Piano One preset in Sunday Keys for Ableton, you'll want to check a few settings.
The issue is related to the remote function being selected for the keyboard input you are using. You may have turned on the remote function if you are wanting to map things in Ableton to your mod wheel, faders, knobs, etc., on your midi keyboard. If this is the case, you will want to make sure to change the MIDI channel of your keyboard, as the default channel 1 MIDI CC 64 (sustain) message is set up to jump to that “OFF” scene.
If you are not mappings any controls to your MIDI keyboard, then you can just turn off the remote function for your midi keyboard in Ableton.
This is covered on the Sunday Keys for Ableton Video Resource page in Video 5 (“Mapping controls to your midi controller/keyboard”) around the 13:20 minute mark.