Slime cannot be moved when there's an unmoveable object/block sticking to it

What i want to do was:
1.Play minecraft
2.Open my snapshot world
3.Make an elevator (with slime and minecarts)
4.Place obsidian (or other unmoveable blocks)
5.Works as intended to be

What i get was:
1.Play minecraft
2.Open my snapshot world
3.Make an elevator (with slime and minecarts)
4.Place obsidian (or other unmoveable blocks)
5.The slimeblock won't move T_T