When you are saving and quitting a world, the game freezes up, and crashes. It also can break worlds due to not saving correctly.
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Please note that this effects MACS and not just PCs

Dupe of MC-65329, seems to come up randomly and without any errors in the console. Sadly i cant reproduce this anymore.

Only seems to happen when I try to close after opening to LAN; does not give crash report (Mac OS X 10.9.4; 14w33c). The game just freezes when I try to hit the "Save and Quit to Title" button. I can move my mouse, etc., but the game doesn't respond, even when I try to hit other buttons in the menu. Only way to fix is to force the game to close and restart the launcher.

Can definitely reproduce, happens 50% of the time when I host LAN worlds. No crash reports.

@@unknown: In 1.8 or 1.8.1-pre3 ? This seems to be related to MC-72806

Using 1.8

This is happening to me every time I try to save and quit on a LAN session as well. I've only noticed this error this last time, so I'm not sure if it's happened every time, but I got the same error as this report MCL-1905. Here's the error report in the Launcher Log (there's no sign of an error in Game Output) (11:48 is when I launched the game, and 13:58 is when I tried to quit):
[11:48:53 FATAL]: Fatal error launching game. Report this to http://bugs.mojang.com please!
java.io.FileNotFoundException: File 'C:\Users\Ben\AppData\Roaming\.minecraft\assets\indexes\legacy.json' does not exist
at org.apache.commons.io.FileUtils.openInputStream(FileUtils.java:299) ~[launcher.jar:?]
at org.apache.commons.io.FileUtils.readFileToString(FileUtils.java:1711) ~[launcher.jar:?]
at net.minecraft.launcher.Launcher.cleanupOrphanedAssets(Launcher.java:252) ~[launcher.jar:?]
at net.minecraft.launcher.Launcher.performCleanups(Launcher.java:494) ~[launcher.jar:?]
at net.minecraft.launcher.game.MinecraftGameRunner.launchGame(MinecraftGameRunner.java:221) ~[launcher.jar:?]
at com.mojang.launcher.game.runner.AbstractGameRunner.onDownloadJobFinished(AbstractGameRunner.java:185) [launcher.jar:?]
at com.mojang.launcher.updater.download.DownloadJob.popAndDownload(DownloadJob.java:122) [launcher.jar:?]
at com.mojang.launcher.updater.download.DownloadJob.access$000(DownloadJob.java:12) [launcher.jar:?]
at com.mojang.launcher.updater.download.DownloadJob$1.run(DownloadJob.java:86) [launcher.jar:?]
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.7.0_65]
at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.7.0_65]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [?:1.7.0_65]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [?:1.7.0_65]
at java.lang.Thread.run(Unknown Source) [?:1.7.0_65]
[13:58:05 ERROR]: Game ended with bad state (exit code -805306369)
[13:58:09 INFO]: Ignoring visibility rule and showing launcher due to a game crash
[13:58:12 INFO]: Deleting C:\Users\Ben\AppData\Roaming\.minecraft\versions\1.8.1\1.8.1-natives-296251035682913
Edit: My next time hosting a LAN world it happened again with the same error.

Marking this as duplicate of MC-72943 would help with new user navigation and search.
Incomplete without a crash report from (
[minecraft/crash-reports/crash-<DATE>-client.txt|http://hopper.minecraft.net/help/finding-minecraft-data-folder]
). Please attach it so that we can diagnose your issue.