I have found a few issues relating to piston events in 1.8.3 Bukkit/Spigot. I am not sure if these exist in the 1.8 version of CraftBukkit/Spigot.

Issues:
#Canceling BlockPistonRetractEvent causes the block that would have been moved to disappear to the client. When walking to where the block should be, you glitch because the block is there but now just invisible until it is left or right clicked.
#The method isSticky() in PistonEvent is returning false even though a sticky piston is being used. This even occurs when you are checking if the piston in the BlockPistonRetractEvent is sticky, it will return false.