I have the latest full version of Minecraft installed (1.5.2), without snapshots or mods (single player mode). The descripted error already appears. The world status, including the recently added items in a chest inventory, is saved incomplete. Waiting a few minutes before leaving the game to the main menu seems to increase the chance of correct saving. But it is not reliable. Please, create a boringly normal, but working save button, even though the game is somewhat less novel.
Once again me. Starting the proposed batch file, minecraft does not start. error.txt then contains the message (in german): "could'nt find or load main class net.minecraft.LauncherFrame". log.txt is empty.
Starting normal works fine. Suggestions?