Writing of grib files loses time dimension

I have the following code (slightly simplified for reproducibility):

import numpy as np
import xarray as xr
from cfgrib.xarray_to_grib import to_grib

# 865_128_256_f32.dat
ntime = 865
nlats = 128
nlons = 256
lats = np.linspace( 0, np.pi, nlats)
lons = np.linspace( 0, np.pi, nlons)
times = list(range( ntime))

vorticity = np.random.randn( ntime, nlats, nlons)

ds2 = xr.DataArray( vorticity, coords=[times, lats, lons],
                        dims=['time', 'latitude', 'longitude'],).to_dataset(name='vo')
ds2.vo.attrs['GRIB_shortName'] = 'vo'

fname_out = 'sh_shallow_vorticity.grib'
to_grib( ds2, fname_out)

ds2 looks correct

>>> ds2 = xr.DataArray( vorticity, coords=[times, lats, lons], dims=['time', 'latitude', 'longitude'],).to_dataset(name='vo')
>>> ds2
<xarray.Dataset>
Dimensions:    (latitude: 128, longitude: 256, time: 8641)
Coordinates:
  * time       (time) int64 0 1 2 3 4 5 6 ... 8634 8635 8636 8637 8638 8639 8640
  * latitude   (latitude) float64 0.0 0.02474 0.04947 ... 3.092 3.117 3.142
  * longitude  (longitude) float64 0.0 0.01232 0.02464 ... 3.117 3.129 3.142
Data variables:
    vo         (time, latitude, longitude) float32 4.53e-05 ... -9.787e-07
>>> ds2.vo.attrs['GRIB_shortName'] = 'vo'
>>> ds2
<xarray.Dataset>
Dimensions:    (latitude: 128, longitude: 256, time: 8641)
Coordinates:
  * time       (time) int64 0 1 2 3 4 5 6 ... 8634 8635 8636 8637 8638 8639 8640
  * latitude   (latitude) float64 0.0 0.02474 0.04947 ... 3.092 3.117 3.142
  * longitude  (longitude) float64 0.0 0.01232 0.02464 ... 3.117 3.129 3.142
Data variables:
    vo         (time, latitude, longitude) float32 4.53e-05 ... -9.787e-07

However, when I re-load the file the time dimension is lost:

>>> xr.open_dataset( '../data/rsw/test/sh_shallow_vorticity.grib', engine='cfgrib')
<xarray.Dataset>
Dimensions:     (latitude: 128, longitude: 256)
Coordinates:
    time        datetime64[ns] ...
    step        timedelta64[ns] ...
    surface     float64 ...
  * latitude    (latitude) float64 0.0 0.02474 0.04947 ... 3.092 3.117 3.142
  * longitude   (longitude) float64 0.0 0.01232 0.02464 ... 3.117 3.129 3.142
    valid_time  datetime64[ns] ...
Data variables:
    vo          (latitude, longitude) float32 ...
Attributes:
    GRIB_edition:            2
    GRIB_centre:             consensus
    GRIB_centreDescription:  Consensus
    GRIB_subCentre:          0
    Conventions:             CF-1.7
    institution:             Consensus
    history:                 2022-06-14T10:26 GRIB to CDM+CF via cfgrib-0.9.1...

ecmwf / cfgrib

Writing of grib files loses time dimension #305