As you can see in the video below, Piston heads CAN NOT push a block ABOVE Y = 128. If the piston itself is at Y = 129, it CAN push down, but it cannot push up.

Tried it in a singleplayer aswell, no changes.
It works perfectly fine below the nether ceiling, but not above

Video:
https://www.youtube.com/watch?v=hnyBEi_8F68&feature=youtu.be