Teams being removed after leaving a World

Ok, if this is a Feature I'm Fine with it, but I was playing on my Singleplayer world on 1.6.1 and I went to 1.5.2 and everytime I leave the world to use NBTEdit the teams get Deleted. It's the same with Health Objectives.
How to commit:
Step 1: go into Minecraft 1.6.1 and create a Team or a health objective
Step 2: Go into Minecraft 1.5.2 and Enter your World
Step 3: Leave the world and Reenter it
Step 4: List the Teams and you find that all the teams are deleted