This issue was originally reported on the Craftbukkit Leaky:
The original reporter was MonsieurApple.
When more than 128 players are online, the array of players will not be sent in response to an RCON query because of a buffer overflow.
This could be fixed by using an int instead of a byte (which has an upward limit of 128) when looping through the list of players.
The issue was closed as outside the scope of CraftBukkit, as the file in that patch does not decompile properly and therefore is unsuitable for inclusion in the project.