SpigotMC/Spigot — pull request #137 by geNAZt (2014-03-18 19:24:55+00:00)
Title: Minecraft allows a length of 20 for the Channel Name not 16

As you can see in the NMS Code here: https://github.com/SpigotMC/mc-dev/blob/master/net/minecraft/server/PacketPlayInCustomPayload.java#L12

The Channel name can have a length of 20. Bukkit limits it to 16 which is wrong