Legato Glide only produces the Glide effect when a new note is played while the previous note is still held down on the keyboard. 

To turn Legato Glide On, continue to press the SHIFT button while turning the GLIDE knob to the right. 

To turn Legato Glide Off, continue to press the SHIFT button while turning the GLIDE knob to the left. The Default setting for Legato Glide is Off.