Bukkit

First of all, when traveling from world to world, It works perfectly, but when you travel from one to another to another, sometimes when you go back one, all the stuff from the first world gets duplicated to the second one.

Second of all, when you go into creative and do something, 90% of the time when you go back into survival, all your stuff is lost.

Third of all, if the server crashes or restarts, all inventories are completely wiped.