Although different transitions act a bit differently this is the generic repro procedure:
1: While still, hold the stance change button.
2: Change stances. Keep both buttons (stance change and direction) held
3: While in the stance change transition animation press and hold another direction that's normal to the change stance button. (If stance change was 'Right', now press and hold 'Forward' or 'Back')
Some animations allow you to continue sliding after keys are released and some require keys to be held to slide.