I was messing around in the new snapshot and found a way to create floating piston heads!
How to Reproduce:
1. Place down a redstone block (perhaps any powering block, not sure)
2. Place any block on any face of the redstone block
3. Place either piston type on the block in step 2
4. Place either type of piston on the redstone block, facing the piston placed in step 3
5. Once the piston in step four extends, destroy its base. The piston head will not be updated. You can remove the other blocks, if desired.
My guess is that this is caused by the way blocks look to other blocks. Perhaps the piston head sees that it's next to a piston base, so it does not need to destroy itself.
Here's a quick video I made demonstrating this bug: