DefaultSpeculator can log the following error message on a normal shutdown of the ApplicationMaster:
2012-11-13 01:35:31,841 ERROR [DefaultSpeculator background processing] org.apache.hadoop.mapreduce.v2.app.speculate.DefaultSpeculator: Background thread returning, interrupted : java.lang.InterruptedException
and in addition for some reason it logs the corresponding backtrace to stdout.
Like the errors fixed in
MAPREDUCE-4741, this error message in the syslog and backtrace on stdout can be confusing to users as to whether the job really succeeded.