The bug
As of 1.9, pistons were considered to have a solid top surface, meaning levers, buttons, flower pots, torches, and the like were able to be placed on them. However, in 17w47b, you can no longer place buttons or levers on top of pistons (flower pots and torches still work).
Linked issues
is duplicated by 1
relates to 2
Comments 7
That was a bug related to those blocks popping off when pistons extend. I'm relatively sure they're still intended to be placed on pistons (I guess the resolution to this bug will determine that), but the issue I'm referring to is that levers and buttons can't be placed on pistons anymore as of this snapshot.
Normally Works As Intended. Originally, it was a bug and it is supposed to work only with flowerpots and torches.
It is the same question with hoppers (see MC-122352).
This may be intended, as originally, it was a bug.
See video : https://www.youtube.com/watch?v=VyUeqeLoOb8