using the new minecart functionality where it is able to display any block, a piston and sticky piston will not rotate in a minecart regardless of data value.
Used MCedit and a filter to change the block to piston and then each minecart has a different data value. As you can see on the screenshot they all look the same. I can confirm the filter does work as it works to rotate pumpkins and it also goes through all the data values of mushroom blocks.
It's just an issue with the magic that is the piston renderer. Won't fix because the minecart display is intended just for basic blocks.