Songs 1-7, 9-20, 29-50,and 69-100 on the EZ20 automatically set the first 19 keys on the left side of the keyboard to different sound effects and musical phrases. This is called the 'Multi Pads' function. To disable this function, the Song must be played using the Lesson 3, 'MinusOne' mode, with the left hand only selected.
1) Press the [SONG] button.
Reference: Owner's Manual, p.35
2) Select a Song using the Numeric Key Pad.
3) Press the [L] button to select the left hand only.
4) Press the  'LESSON' button. The Song will begin to play in 'MinusOne' mode. The left hand will now control the Accompaniment chords, and Multi Pad sounds will not be triggered.