I wrote down a long message in a commandblock, and both using /tell and /say it doesn't show the entire message when I'm using a multiplayer server. But when I use bukkit or single player, it does show the entire message. Even when I'm using open to LAN it shows the entire message.

how to reproduce:
-make a commandblock and put in /say <message longer than 112 characters>
-power the command block in Single Player you'll see the entire message
-power the command block using the server downloaded from minecraft.net and you won't see the entire message.