resource:redshift-snapshot tag policy failing

[ajohnstone]

$ custodian run --debug --cache-period 0 --cache 0   -s out x.yaml
2017-10-25 21:22:37,492: custodian.policy:INFO policy: redshift-snapshot-tag-policy resource:redshift-snapshot region:eu-west-1 count:823 time:14.91
2017-10-25 21:22:37,668: custodian.actions:ERROR Exception with tags: [{u'Value': 'bi@abc.com', u'Key': 'Owner'}] on resources: rs:cloud-dwh-2017-10-25-15-10-38, rs:cloud-dwh-2017-10-24-09-10-31, rs:cloud-dwh-2017-10-20-23-40-50 
 u'SnapshotIdentifer'
2017-10-25 21:22:37,681: custodian.actions:ERROR Exception with tags: [{u'Value': 'bi@abc.com', u'Key': 'Owner'}] on resources: rs:cloud-dwh-2017-10-25-15-10-38, rs:cloud-dwh-2017-10-24-09-10-31, rs:cloud-dwh-2017-10-20-23-40-50 
 u'SnapshotIdentifer'

example

policies:
  - name: redshift-snapshot-tag-policy
    resource: redshift-snapshot
    comments: |
      Create tags for redshift-snapshot with bi
    filters:
      - or:
        - "tag:Owner": absent
        - "tag:Department": absent
    actions:
      - type: tag
        key: Owner
        value: bi@abc.com
      - type: tag
        key: Department
        value: bi