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
1318992926,I_kwDOAMm_X85Onjwe,6836,groupby(multi-index level) not working correctly on a multi-indexed DataArray or DataSet,5643062,closed,0,4160723,,9,2022-07-27T04:06:59Z,2023-06-06T00:21:32Z,2023-06-06T00:21:32Z,NONE,,,,"### What happened?

run the code block below with `2022.6.0`
```
midx = pd.MultiIndex.from_product([list(""abc""), [0, 1]], names=(""one"", ""two""))

mda = xr.DataArray(np.random.rand(6, 3), [(""x"", midx), (""y"", range(3))])

mda.groupby(""one"").groups
```
output:
```
In [15]: mda.groupby(""one"").groups
Out[15]: 
{('a', 0): [0],
 ('a', 1): [1],
 ('b', 0): [2],
 ('b', 1): [3],
 ('c', 0): [4],
 ('c', 1): [5]}
```

### What did you expect to happen?

as it was with `2022.3.0`
```
In [6]: mda.groupby(""one"").groups
Out[6]: {'a': [0, 1], 'b': [2, 3], 'c': [4, 5]}
```

### Minimal Complete Verifiable Example

```Python
import pandas as pd
import numpy as np
import xarray as XR

midx = pd.MultiIndex.from_product([list(""abc""), [0, 1]], names=(""one"", ""two""))

mda = xr.DataArray(np.random.rand(6, 3), [(""x"", midx), (""y"", range(3))])

mda.groupby(""one"").groups
```


### MVCE confirmation

- [X] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
- [X] Complete example — the example is self-contained, including all data and the text of any traceback.
- [X] Verifiable example — the example copy & pastes into an IPython prompt or [Binder notebook](https://mybinder.org/v2/gh/pydata/xarray/main?urlpath=lab/tree/doc/examples/blank_template.ipynb), returning the result.
- [X] New issue — a search of GitHub Issues suggests this is not a duplicate.

### Relevant log output

```Python
N/A
```


### Anything else we need to know?

N/A

### Environment

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.8.10 (default, Mar 15 2022, 12:22:08) 
[GCC 9.4.0]
python-bits: 64
OS: Linux
OS-release: 5.11.0-1025-aws
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: C.UTF-8
LOCALE: ('en_US', 'UTF-8')
libhdf5: 1.12.0
libnetcdf: 4.7.4

xarray: 2022.6.0
pandas: 1.4.3
numpy: 1.22.4
scipy: 1.7.3
netCDF4: 1.5.8
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: 1.5.1.1
nc_time_axis: None
PseudoNetCDF: None
rasterio: 1.2.10
cfgrib: None
iris: None
bottleneck: 1.3.2
dask: 2022.04.1
distributed: 2022.4.1
matplotlib: 3.5.1
cartopy: 0.20.3
seaborn: 0.11.2
numbagg: None
fsspec: 2022.01.0
cupy: None
pint: None
sparse: None
flox: None
numpy_groupies: None
setuptools: 45.2.0
pip: 22.2
conda: None
pytest: 7.1.2
IPython: 7.31.0
sphinx: None
</details>
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