I'd like to remove a label from node using strategic merge patch. Here is what I used to remove label:

kubectl patch node xxx --type='strategic' -p '{"metadata":{"labels":{"$patch": "delete", "node-role.kubernetes.io/master":""}}}'
xxx patched

It succeeded but there are two issues here:

1. It removed all labels but not only the label I specified.
2. When I tried to patch it again on same node, it reported error:

kubectl patch node xxx --type='strategic' -p '{"metadata":{"labels":{"$patch": "delete", "node-role.kubernetes.io/master":""}}}'
The Node "xxx" is invalid: metadata.labels: Invalid value: "$patch": name part must consist of alphanumeric characters, '-', '_' or '.', and must start and end with an alphanumeric character (e.g. 'MyName',  or 'my.name',  or '123-abc', regex used for validation is '([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9]')

How should I only remove one label I specified? The patch with delete operation is not idempotent? I don't quite understand the error it reported when I tried to delete the label again.