1.3.1 bukkit server "world" just load up

so pretty much what happens is i start up my bukkit server fine everything is running perfect until i join or anyone joins and finds that the world has not loaded or is loading in pieces. so what i tried was i downgraded to 1.2.5 nd tried and it worked perfectly fine. i even checked it in single player and the world was working perfectly. so im wondering what might be wrong. can anyone help me ?