Just for the record, I just ran into this for the specific case of nested dictionary attrs in Dataarray.attrs.

It's definitely an issue in 2022.3.0 and 2022.6.0. Here's a minimal test example in case anyone else runs into this too...

```python

MINIMAL EXAMPLE

import xarray as xr import numpy as np

data = xr.DataArray(np.random.randn(2, 3), dims=("x", "y"), coords={"x": [10, 20]}) data.attrs['flat']='0' data.attrs['nested']={'level1':'1'}

data2 = data.copy(deep=True) data2.attrs['flat']='2' # OK

data2.attrs['nested']={'level1':'2'} # OK

data2.attrs['nested']['level1'] = '2' # Fails - overwrites data

data2.attrs['nested'].update({'level1':'2'}) # Fails - overwrites data

print(data.attrs) print(data2.attrs) ```

Outputs

In XR 2022.3.0 and 2022.6.0 this gives (incorrect): ``` {'flat': '0', 'nested': {'level1': '2'}} {'flat': '2', 'nested': {'level1': '2'}}

```

As a work-around, safe attrs copy with deepcopy works:

```python data2 = data.copy(deep=True) data2.attrs = copy.deepcopy(data.attrs)

```

With correct results after modification: ``` {'flat': '0', 'nested': {'level1': '1'}} {'flat': '2', 'nested': {'level1': '2'}}

```

EDIT 26th Sept: retested in 2022.6.0 and found it was, in fact, failing there too. Updated comment to reflect this.