Docker bug with ENTRYPOINT and CMD

Dockerfile

FROM dockerfile/python

ADD / /build

ENTRYPOINT ["/build/foo.py"]
# output: args ['/build/foo.py', 'bash']

# None of these work as expected either

#CMD ['arg1']
# output: args ['/build/foo.py', '/bin/sh', '-c', "['arg1']"]

#CMD ['arg1', 'arg2']
# output: args ['/build/foo.py', '/bin/sh', '-c', "['arg1', 'arg2']"]

#CMD 'arg1 arg2'
# output: args ['/build/foo.py', '/bin/sh', '-c', "'arg1 arg2'"]

foo.py

#!/usr/bin/env python

import sys
print 'args', sys.argv