Why the values of 'ulimit -c' are different between bash and sh.

Issue

• ulimit -c returns abnormal value:

  # cat /etc/security/limits.conf
  * soft core 10000
  # ulimit -c
  10000
  # sh 
  sh-4.1# ulimit -c                        
  20000                           <------return abnormal value
  sh-4.1# bash
  # ulimit -c
  10000