I don't know why those people at Bukkit (or whatever the fuck they name it) think that they can just remove things of vanilla Minecraft without causing Problems. Why do people even make Bukkit Plugins if it causes so many Problems to even have Bukkit installed, especially since Forge alone has ALL Functionality Bukkit provides. World Guard? No Problem just use Forge instead, like many Force Field Mods do successfully already. Multi World? If Mystcraft can easyly do other Dimensions using Forge, then it should work for something as simple as that too. Seriously, there is no need for Bukkit or Cauldron or whatever that is called at all.
Simple. Cauldron has APIs that Forge lacks. Monitoring APIs. I don't know specifics, but its all API issues afaik.