I use a stone pressure plate on the inside of my house in order to open my (iron) front door when leaving. But after downloading the snapshot, I found that stepping on the stone pressure plate wasn't activating the door. I tried picking it up and placing it on multiple spots on the ground, but it still wouldn't depress, and the activation sound didn't play. I replaced its place against the door with a wooden pressure plate, which worked fine. I did some testing in Creative Mode, and got the same results: Wooden pressure plates are all functioning as normal, but stone ones can't activate doors, TNT, and other redstone-enabled devices.