io.sort.factor code default and mapred-default.xml values inconsistent

<property>
  <name>mapreduce.task.io.sort.factor</name>
  <value>10</value>
  <description>The number of streams to merge at once while sorting
  files.  This determines the number of open file handles.</description>
</property>

       
 int mergeFactor = job.getInt(JobContext.IO_SORT_FACTOR, 100);