Why CPU affinity of a process set by "taskset" command getting reset automatically ?

Issue

• CPU affinity of a process is set to 15-14 using "taskset" command.
  Eg:

# taskset -c 15-14 ./test.sh > /tmp/test.log 2>&1 &

• Initially it is giving the expected result (i.e task is always using cpus 14-15 )

Wed Nov 6 15:17:26 EST 2013
 15 67959 54796 \_ test.sh
 14 54796 54799 \_ ps
Wed Nov 6 15:22:26 EST 2013
 14 67959 54796 \_ test.sh
 15 54796 55375 \_ ps 

• But after ~12 hours, the affinity is getting reset and the CPUs reported changed.

Thu Nov 7 03:52:30 EST 2013 
 15 67959 54796 \_ test.sh 
 14 54796 53895 | \_ ps  
Thu Nov 7 03:57:30 EST 2013         
  8 67959 54796 \_ test.sh 
 10 54796 55026 | \_ ps 
Thu Nov 7 04:02:30 EST 2013 
  8 67959 54796 \_ test.sh 
 10 54796 55561 | \_ ps