Affects Version/s: Snapshot 13w02b
Fix Version/s: None
Environment:Java version "1.7.0_09"
Windows 7 Professional
A few variations possible of the bug, using both the redstone block and any block with a redstone torch below, depending on if only one piston is sticky or if both are, there are two differences.
If there is a sticky and a regular piston, the block disappears and the pistons pulse rapidly, both of the redstone wire outputs a 1-tick pulse. Reloading the world/chunks can cause one of the pistons to "hold" onto the block, even though there is visible redstone power leading into the piston.
If both the pistons are sticky, the block in between gets pulled in between a block where it was placed, so it is not within the typical position (some of the way between the 2 block gap), the piston head sometimes clips through the block. Reloading world/chunks did not appear to cause the same action as above.
Also, using torches below a block instead of a redstone block adds another strange action on survial mode. If you jump into the pistons, you will stay off the ground, have extremely slow movement speed, and if you stay there for a while and then walk off, you hear the fall damage noise but take no damage.
I have included some screenshots of these 3 different set-ups, and I will explain how to set this up.
1. Place 2 pistons facing each other with a 2 block gap in between.
2. Place a redstone block / block with 2 torches below in the gaps.
3. Connect redstone wire to the block to the piston.