open_mfdataset overwrites variables with different values but overlapping coordinates

In the example below I'm opening and concatenating two datasets using open_mfdataset. These datasets have variables with different values but overlapping coordinates. I'm concatenating along y, which is 0...4 in one dataset and 0...5 in the other. The y dimension of the resulting dataset is 0...5 which means that open_mfdataset has overwritten some values without showing any error/warning.

Is this the expected default behavior? I would expect to get at least a warning, but maybe I'm misunderstanding the default arguments.

I tried to play with the arguments, but I couldn't figure out which argument I should change to get an error in these scenarios.

MCVE Code Sample

import xarray as xr
import numpy as np

for i in range(2):
    ds = xr.Dataset(
        {"foo": (("x", "y"), np.random.rand(4, 5 + i))},
        coords={"x": np.arange(4), "y": np.arange(5 + i)},
    )
    print(ds)
    ds.to_netcdf(f"tmp{i}.nc")

<xarray.Dataset>
Dimensions:  (x: 4, y: 5)
Coordinates:
  * x        (x) int64 0 1 2 3
  * y        (y) int64 0 1 2 3 4
Data variables:
    foo      (x, y) float64 0.1271 0.6117 0.3769 0.1884 ... 0.853 0.5026 0.3762
<xarray.Dataset>
Dimensions:  (x: 4, y: 6)
Coordinates:
  * x        (x) int64 0 1 2 3
  * y        (y) int64 0 1 2 3 4 5
Data variables:
    foo      (x, y) float64 0.2841 0.6098 0.7761 0.0673 ... 0.2954 0.7212 0.3954

DS = xr.open_mfdataset("tmp*.nc", concat_dim="y", combine="by_coords")
print(DS)

<xarray.Dataset>
Dimensions:  (x: 4, y: 6)
Coordinates:
  * x        (x) int64 0 1 2 3
  * y        (y) int64 0 1 2 3 4 5
Data variables:
    foo      (x, y) float64 dask.array<chunksize=(4, 6), meta=np.ndarray>

Versions

Start by running the MCVE that writes tmp0.nc and tmp1.nc, then inspect the open_mfdataset call with concat_dim="y" and combine="by_coords". Compare the overlapping foo values in the two datasets and determine whether the overwrite is expected. Done should establish the supported behavior and identify how an error or warning can be requested, if available.