When sticky pistons are placed diagonally below a redstone block, they do not behave correctly. They will extend when not adjacent to the redstone block when facing any direction as long as they are below the redstone block. They will remain extended if the redstone block is removed, and will only retract when the block is updated. Placing sticky pistons above a redstone block in this manner will not cause them to extend. This issue also affects regular pistons.