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
955617411,MDU6SXNzdWU5NTU2MTc0MTE=,5646,Level names in multi-level index are ignored,688461,closed,0,,,3,2021-07-29T08:56:48Z,2022-09-27T12:34:21Z,2022-09-27T12:34:20Z,NONE,,,,"**What happened**:
The difference of the level names in multi-level index is silently ignored.

**What you expected to happen**:
Error message.

**Minimal Complete Verifiable Example**:

```python
import xarray as xr

a = xr.DataArray([[1]], dims = [""x"", ""y""])

b = a.stack({""z"": [""x"", ""y""]})
c = a.rename({""x"": ""not-x"", ""y"": ""not-y""}).stack({""z"": [""not-x"", ""not-y""]})

xr.testing.assert_allclose(b, c)
print(b == c, ""\n"")
print(b.coords == c.coords, ""\n"")
print(b + c, ""\n"")
print(c + b, ""\n"")
```

Output:
```
<xarray.DataArray (z: 1)>
array([ True])
Coordinates:
  * z        (z) MultiIndex
  - x        (z) int64 0
  - y        (z) int64 0

True

<xarray.DataArray (z: 1)>
array([2])
Coordinates:
  * z        (z) MultiIndex
  - x        (z) int64 0
  - y        (z) int64 0

<xarray.DataArray (z: 1)>
array([2])
Coordinates:
  * z        (z) MultiIndex
  - not-x    (z) int64 0
  - not-y    (z) int64 0

```

**Environment**:

<details><summary>Output of <tt>xr.show_versions()</tt></summary>

INSTALLED VERSIONS
------------------
commit: None
python: 3.9.1 (tags/v3.9.1:1e5d33e, Dec  7 2020, 17:08:21) [MSC v.1927 64 bit 
(AMD64)]
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 165 Stepping 5, GenuineIntel
byteorder: little
LC_ALL: None
LANG: ru_RU.UTF-8
LOCALE: ('Russian_Russia', '1251')
libhdf5: 1.12.0
libnetcdf: None

xarray: 0.18.2
pandas: 1.3.0
numpy: 1.21.1
scipy: 1.6.0
netCDF4: None
pydap: None
h5netcdf: None
h5py: 3.1.0
Nio: None
zarr: None
cftime: None
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: None
distributed: None
matplotlib: 3.4.2
cartopy: None
seaborn: None
numbagg: None
pint: None
setuptools: 57.4.0
pip: 21.1.3
conda: None
pytest: None
IPython: None
sphinx: None

</details>
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