When I closed a world, the following happened in the console:

[11:41:45 INFO]: Client> [11:41:45] [Server thread/INFO]: Stopping server
[11:41:45 INFO]: Client> [11:41:45] [Server thread/INFO]: Saving players
[11:41:45 INFO]: Client> [11:41:45] [Server thread/INFO]: Saving worlds
[11:41:45 INFO]: Client> [11:41:45] [Server thread/INFO]: Saving chunks for level 'Whil E. Coyote'/Overworld
[11:41:45 INFO]: Client> [11:41:45] [Server thread/INFO]: Saving chunks for level 'Whil E. Coyote'/Nether
[11:41:45 INFO]: Client> [11:41:45] [Server thread/INFO]: Saving chunks for level 'Whil E. Coyote'/The End
[11:41:45 INFO]: Client> java.io.IOException: Stream Closed
[11:41:45 INFO]: Client> at java.io.RandomAccessFile.seek(Native Method)
[11:41:45 INFO]: Client> at avb.a(SourceFile:313)
[11:41:45 INFO]: Client> at avb.a(SourceFile:253)
[11:41:45 INFO]: Client> at avc.close(SourceFile:234)
[11:41:45 INFO]: Client> at java.util.zip.DeflaterOutputStream.close(Unknown Source)
[11:41:45 INFO]: Client> at java.io.FilterOutputStream.close(Unknown Source)
[11:41:45 INFO]: Client> at ave.a(SourceFile:148)
[11:41:45 INFO]: Client> at ave.c(SourceFile:136)
[11:41:45 INFO]: Client> at ber.b(SourceFile:32)