Slime bug contraptions do not work in pocket edition 1.4.4

Slime block lifts and slime block vehicles do not work as designed or as shown on youtube videos. They should go in one direction and only stop when they hit an immovable block or the ground. Instead they are randomly changing direction and occassionally some bits disappear and reappear or simply let you fall through. This happens on my LG V20 AND my lenovo tablet and my hudl 2