When using snapshot 17w13a pistons don't appear to animate correctly, instead the seem to just switch between retracted and extended.
Example of what I'm talking about: https://gfycat.com/AnguishedFaroffBunny
Environment
OS: Windows 10 Build 14393.969
java -version
java version "1.8.0_60"
Java(TM) SE Runtime Environment (build 1.8.0_60-b27)
Java HotSpot(TM) 64-Bit Server VM (build 25.60-b23, mixed mode)
Graphics: AMD Radeon 7970, Driver version 16.50.2001-161204a-309270C
Most likely MC-114881, moving pistons are block entities.