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.