When you open a old world (from 1.7) in this new snapshot, this world crash and corrupt files.
Environment
[18:19:40 INFO]: System.getProperty('os.name') == 'Windows 8.1'
[18:19:40 INFO]: System.getProperty('os.version') == '6.3'
[18:19:40 INFO]: System.getProperty('os.arch') == 'amd64'
[18:19:40 INFO]: System.getProperty('java.version') == '1.8.0'
[18:19:40 INFO]: System.getProperty('java.vendor') == 'Oracle Corporation'
[18:19:40 INFO]: System.getProperty('sun.arch.data.model') == '64'
Dupe of MC-61032