issue in saving monthly restart files

[wfc1102@163_com]

CESM version: cesm1_1_1_lrg_ens
compset: B1850C5CN
res: f09_g16

I want to run for one year with monthly restart files by setting as below
STOP_N = 1
STOP_OPTION = nmonths
REST_N = 1
REST_OPTION = nmonths
DOUT_S_SAVE_INT_REST_FILES = TRUE
RESUBMIT = 11

What I got under archive directory is
2020-01-01-00000/EXP.cam.i.2020-01-01-00000.nc
2020-02-01-00000/EXP.cam.i.2020-01-01-00000.nc
2020-03-01-00000/EXP.cam.i.2020-01-01-00000.nc
2020-04-01-00000/EXP.cam.i.2020-01-01-00000.nc
2020-05-01-00000/EXP.cam.i.2020-01-01-00000.nc
2020-06-01-00000/EXP.cam.i.2020-01-01-00000.nc
2020-07-01-00000/EXP.cam.i.2020-01-01-00000.nc
2020-08-01-00000/EXP.cam.i.2020-01-01-00000.nc
2020-09-01-00000/EXP.cam.i.2020-01-01-00000.nc
2020-10-01-00000/EXP.cam.i.2020-01-01-00000.nc
2020-11-01-00000/EXP.cam.i.2020-01-01-00000.nc
2020-12-01-00000/EXP.cam.i.2020-01-01-00000.nc
All these cam.i files above are the same.

However other restart files looks fine:
2020-01-01-00000/EXP.cam.r.2020-01-01-00000.nc
2020-02-01-00000/EXP.cam.r.2020-02-01-00000.nc
2020-03-01-00000/EXP.cam.r.2020-03-01-00000.nc
2020-04-01-00000/EXP.cam.r.2020-04-01-00000.nc
2020-05-01-00000/EXP.cam.r.2020-05-01-00000.nc
2020-06-01-00000/EXP.cam.r.2020-06-01-00000.nc
2020-07-01-00000/EXP.cam.r.2020-07-01-00000.nc
2020-08-01-00000/EXP.cam.r.2020-08-01-00000.nc
2020-09-01-00000/EXP.cam.r.2020-09-01-00000.nc
2020-10-01-00000/EXP.cam.r.2020-10-01-00000.nc
2020-11-01-00000/EXP.cam.r.2020-11-01-00000.nc
2020-12-01-00000/EXP.cam.r.2020-12-01-00000.nc
2021-01-01-00000/EXP.cam.r.2021-01-01-00000.nc

Thus, I wonder why cam.i only saved the start time of the year, 01-01, not the start time of each month, 02-01, 03-01, etc?
Any suggestions are appreciated, many thanks.