[ferret_users] How to cancel attribute strange issue

I have one strange issue with ferret. I am writing date and time as a string to file. Before writing to file I can't find attribute name "long_name_mod " in both variable date and time

This is before Writing to file

yes? show att/all date
attributes for user-defined variables
Date.long_name = Date - String
Date.missing_value = -1.E+34
Date.units = DD:MM:YR

yes? show att/all time
attributes for user-defined variables
Time.long_name = UTC - String
Time.missing_value = -1.E+34
Time.units = HH:MN

After writing to file

     NOAA/PMEL TMAP
     FERRET v6.842
     Linux 2.6.32-279.19.1.el6.x86_64 32-bit - 02/01/13
     2-Nov-13 18:54

yes? use test.nc
yes? sh d
     currently SET data sets:
    1> ./test.nc (default)
name     title                             I         J         K         L         M         N
DATE     Date - String                    1:10      ...       ...       ...       ...       ...
       (X=0.5:10.5)
TIME     UTC - String                     1:10      ...       ...       ...       ...       ...
       (X=0.5:10.5)

yes? show att/all date
     attributes for dataset: ./test.nc
DATE.long_name = Date - String
DATE.units = DD:MM:YR
DATE.long_name_mod = X=0.5:10.5
yes? show att/all time
     attributes for dataset: ./test.nc
TIME.long_name = UTC - String
TIME.units = HH:MN
TIME.long_name_mod = X=0.5:10.5

akshay@aix:~/Desktop/test$ ncdump -c test.nc
netcdf test {
dimensions:
    PROFILE = "" ;
    STRING1_17 = 17 ;
variables:
    double PROFILE(PROFILE) ;
        PROFILE:point_spacing = "even" ;
        PROFILE:axis = "X" ;
    char DATE(PROFILE, STRING1_17) ;
        DATE:long_name = "Date - String" ;
        DATE:units = "DD:MM:YR" ;
        DATE:long_name_mod = "X=0.5:10.5" ;
    char TIME(PROFILE, STRING1_17) ;
        TIME:long_name = "UTC - String" ;
        TIME:units = "HH:MN" ;
        TIME:long_name_mod = "X=0.5:10.5" ;

// global attributes:
        :history = "FERRET V6.842    2-Nov-13" ;
        :Conventions = "CF-1.0" ;
data:

PROFILE = "" 2, 3, 4, 5, 6, 7, 8, 9, 10 ;
}

I don't want attribute long_name_mod and I don't want rewrite to file again. Any solution ??

- Akshay