When using Spigot 1.9 make sure you use the latest development build of ProtocolLib. You can download it from
http://ci.dmulloy2.net/job/ProtocolLib/. (Use them at your own risk!)
Minor fixes for Spigot 1.9 (Only plugin statistic client was affected, old version works fine too!)
Updating on older versions than 1.9 or other platforms (e.g. BungeeCord) is not necessary.