13w04a server, command block bug

When on a 13w04a snapshot server(not on singleplayer or with open to lan) using command blocks, if you have a command block do /give @p 310 it will corrupt your user file. also /give @p 311 it will give you the diamond chestplate but it will auto apply as a helmet. It does this on both creative and survival. This needs to be fixed.