CDO

Hello, I'd like to concatenate 2 netcdf files with timeseries data. I've done some trials and now I think I know how to make it work, but my question is why it wouldn't work with my initial netcdf.

Initial netcdf:
$ ncdump -v TIME infile.nc

dimensions:
    LATITUDE = 100 ;
    LONGITUDE = 80 ;
    TIME = UNLIMITED ; // (12 currently)
variables:
    float LATITUDE(LATITUDE) ;
        LATITUDE:UNITS = "DEGREES_NORTH" ;
    float LONGITUDE(LONGITUDE) ;
        LONGITUDE:UNITS = "DEGREES_EAST" ;
    float TIME(TIME) ;
        TIME:UNITS = "hour since 2011-06-01 00:00:00" ; # in second file: TIME:UNITS = "hour since 2011-06-01 12:00:00" ;
         TIME:time_origin = "2011-06-01 00:00:00" ; # in second file: TIME:time_origin = "2011-06-01 12:00:00" 
...
data:
 TIME = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ;

Now when I concatenate 2 files, one starting at 00 hour and another at 12, it doesn't add another 12 hours, from 13 to 24, but duplicates hours 1 to 12:

Snippets of results for 'ncdump -v TIME outfile' of commands:
$ cdo mergetime infile outfile
TIME = 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11,
12, 12 ;
$ cdo cat infile outfile
TIME = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12 ;
$ cdo copy infile outfile
TIME = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12 ;

Result of 'cdo showdate' for output files produced by cdo cat and copy:
$ cdo showdate outfile.nc
0000-00-01 0000-00-02 0000-00-03 0000-00-04 0000-00-05 0000-00-06 0000-00-07 0000-00-08 0000-00-09 0000-00-10 0000-00-11 0000-00-12 0000-00-01 0000-00-02 0000-00-03 0000-00-04 0000-00-05 0000-00-06 0000-00-07 0000-00-08 0000-00-09 0000-00-10 0000-00-11 0000-00-12
cdo mergetime:
$ cdo showdate outfile_mergetime.nc
0000-00-01 0000-00-02 0000-00-03 0000-00-04 0000-00-05 0000-00-06 0000-00-07 0000-00-08 0000-00-09 0000-00-10 0000-00-11 0000-00-12

To make it work as I need and expected it initially, I run this command for every file, before using any of the concatenating command:

$ cdo setreftime,2011-06-01,00:00:00,hours -settaxis,2011-06-01,01:00:00,1hour -setcalendar,standard infile.nc outfile.nc

After running this command, mergetime, copy and cat seems to work as expected, they create 24h files with proper dates and times.
However, some properties of netcdf file are changed.

Variables in initial netcdf file:

float LATITUDE(LATITUDE) ;
         LATITUDE:UNITS = "DEGREES_NORTH" ;
    float LONGITUDE(LONGITUDE) ;
        LONGITUDE:UNITS = "DEGREES_EAST" ;

changed to:

float LONGITUDE(LONGITUDE) ;
        LONGITUDE:axis = "X" ;
    float LATITUDE(LATITUDE) ;
        LATITUDE:axis = "Y" ;

and:

    float TIME(TIME) ;
        TIME:UNITS = "hour since 2011-06-01 00:00:00" ;
        TIME:time_origin = "2011-06-01 00:00:00" ;

changed to:

    double time(time) ;
        time:standard_name = "time" ;
        time:units = "hours since 2011-6-1 00:00:00" ;
        time:calendar = "proleptic_gregorian" ;
        time:axis = "T" ;

Was there something incompatible with current cdo or netcdf in my initial netcdf files?
Do I have to run setrefaxis and settaxis to make it work, or is there any simpler way? Maybe just change TIME:UNIT string?
Why it changes my initial variables desctiption, that didn't seem to be touched by those commands? Can I keep them the old way somehow?
Is there something wrong with my initial time units: 'TIME:UNITS = "hour since 2011-06-01 00:00:00" ;'?

Regards,
Pawel