id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
510844652,MDU6SXNzdWU1MTA4NDQ2NTI=,3432,Scalar slice of MultiIndex is turned to tuples,1200058,closed,0,,,5,2019-10-22T18:55:52Z,2022-03-17T17:11:41Z,2022-03-17T17:11:41Z,NONE,,,,"Today I updated to `v0.14` of xarray and it broke some of my code.

I tried to select one observation of the following dataset:
```
<xarray.Dataset>
Dimensions:       (genes: 31523, observations: 236)
Coordinates:
  * genes         (genes) object 'ENSG00000227232' ... 'ENSG00000232254'
  * observations  (observations) MultiIndex
  - individual    (observations) object 'GTEX-111YS' ... 'GTEX-ZXG5'
  - subtissue     (observations) object 'Whole_Blood' ... 'Whole_Blood'
Data variables:
    [...]
```
`ds.isel(observations=1)`:
```
<xarray.Dataset>
Dimensions:       (genes: 31523)
Coordinates:
  * genes         (genes) object 'ENSG00000227232' ... 'ENSG00000232254'
    observations  object ('GTEX-1122O', 'Whole_Blood')
Data variables:
    [...]
```

As you can see, observations is now a tuple of `('GTEX-1122O', 'Whole_Blood')`.
However, the individual and the subtissue should be kept as coordinates.

#### Output of ``xr.show_versions()``
<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.7.4 (default, Aug 13 2019, 20:35:49) 
[GCC 7.3.0]
python-bits: 64
OS: Linux
OS-release: 3.10.0-514.16.1.el7.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8
libhdf5: 1.10.4
libnetcdf: 4.6.1

xarray: 0.14.0
pandas: 0.25.1
numpy: 1.17.2
scipy: 1.3.1
netCDF4: 1.4.2
pydap: None
h5netcdf: 0.7.4
h5py: 2.9.0
Nio: None
zarr: 2.3.2
cftime: 1.0.3.4
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: 2.5.2
distributed: 2.5.2
matplotlib: 3.1.1
cartopy: None
seaborn: 0.9.0
numbagg: None
setuptools: 41.4.0
pip: 19.2.3
conda: None
pytest: 5.0.1
IPython: 7.8.0
sphinx: None

</details>
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