Incompatibility with `aws s3 cp` client - missing headers on HEAD responses about s3ninja HOT 6 CLOSED

2016-01-14 10:00:19,170 - MainThread - botocore.endpoint - DEBUG - Sending http request: <PreparedRequest [HEAD]>
2016-01-14 10:00:19,171 - MainThread - botocore.vendored.requests.packages.urllib3.connectionpool - INFO - Starting new HTTP connection (1): s3
2016-01-14 10:00:19,184 - MainThread - botocore.vendored.requests.packages.urllib3.connectionpool - DEBUG - "HEAD /s3/mytestbucket/newfile HTTP/1.1" 200 0
2016-01-14 10:00:19,185 - MainThread - botocore.parsers - DEBUG - Response headers: {'content-length': '0', 'server': '6a02b91e2db8 (scireum SIRIUS - powered by Netty)', 'connection': 'keep-alive', 'etag': '249C850F62EA50FEB918B095FC56D763', 'p3p': 'CP="This site does not have a p3p policy."', 'content-md5': 'JJyFD2LqUP65GLCV/FbXYw==', 'content-type': 'text/plain'}
2016-01-14 10:00:19,185 - MainThread - botocore.parsers - DEBUG - Response body:

2016-01-14 10:00:19,186 - MainThread - botocore.hooks - DEBUG - Event needs-retry.s3.HeadObject: calling handler <botocore.retryhandler.RetryHandler object at 0x7f47e835d090>
2016-01-14 10:00:19,186 - MainThread - botocore.retryhandler - DEBUG - No retry needed.
2016-01-14 10:00:19,187 - MainThread - botocore.hooks - DEBUG - Event after-call.s3.HeadObject: calling handler <function enhance_error_msg at 0x7f47e89d4b90>
2016-01-14 10:00:19,187 - MainThread - botocore.hooks - DEBUG - Event after-call.s3.HeadObject: calling handler <awscli.errorhandler.ErrorHandler object at 0x7f47e89a1290>
2016-01-14 10:00:19,187 - MainThread - awscli.errorhandler - DEBUG - HTTP Response Code: 200
2016-01-14 10:00:19,187 - MainThread - awscli.customizations.s3.s3handler - DEBUG - Exception caught during task execution: 'LastModified'
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/awscli/customizations/s3/s3handler.py", line 101, in call
    total_files, total_parts = self._enqueue_tasks(files)
  File "/usr/lib/python2.7/site-packages/awscli/customizations/s3/s3handler.py", line 179, in _enqueue_tasks
    for filename in files:
  File "/usr/lib/python2.7/site-packages/awscli/customizations/s3/fileinfobuilder.py", line 31, in call
    for file_base in files:
  File "/usr/lib/python2.7/site-packages/awscli/customizations/s3/filegenerator.py", line 142, in call
    for src_path, extra_information in file_iterator:
  File "/usr/lib/python2.7/site-packages/awscli/customizations/s3/filegenerator.py", line 314, in list_objects
    yield self._list_single_object(s3_path)
  File "/usr/lib/python2.7/site-packages/awscli/customizations/s3/filegenerator.py", line 362, in _list_single_object
    last_update = parse(response['LastModified'])
KeyError: 'LastModified'