prefix argument doesnt give error if used with object in swift download command

Using 'prefix' optional argument with 'swift download container object' should give error as 'prefix' argument is only supported with 'swift download container'

In following example I have shown the usage of prefix then at the end command where error handling should have been there

# ls
#
# swift download Container1 --prefix t
test-file1 [auth 0.150s, headers 0.217s, total 0.218s, 0.000 MB/s]
test-file3 [auth 0.130s, headers 0.310s, total 0.310s, 0.000 MB/s]
test-file2 [auth 0.165s, headers 0.315s, total 0.315s, 0.000 MB/s]
test-file4 [auth 0.111s, headers 0.331s, total 0.331s, 0.000 MB/s]
# ls
test-file1 test-file2 test-file3 test-file4
#
# swift upload testContainer test-file*
test-file4
test-file3
test-file2
test-file1
# ls
test-file1 test-file2 test-file3 test-file4
# swift list testContainer
test-file1
test-file2
test-file3
test-file4
# rm -rf *
# ls
#
#
# swift download testContainer --prefix s
# swift download testContainer --prefix t
test-file1 [auth 0.110s, headers 0.195s, total 0.196s, 0.000 MB/s]
test-file4 [auth 0.162s, headers 0.228s, total 0.228s, 0.000 MB/s]
test-file3 [auth 0.183s, headers 0.250s, total 0.250s, 0.000 MB/s]
test-file2 [auth 0.149s, headers 0.257s, total 0.257s, 0.000 MB/s]
# rm -rf test-file*
# ls
#
----------------------------------------
Below is the issue, where error was expected
---------------------------------------
#
# swift download testContainer test-file1 --prefix s
test-file1 [auth 0.272s, headers 0.851s, total 0.852s, 0.000 MB/s]
# swift download testContainer test-file1 --prefix t
test-file1 [auth 0.314s, headers 0.386s, total 0.386s, 0.000 MB/s]
# swift download testContainer test-file1 --prefix t test-file2
test-file2 [auth 0.277s, headers 0.363s, total 0.364s, 0.000 MB/s]
test-file1 [auth 0.316s, headers 0.651s, total 0.651s, 0.000 MB/s]
#

I have tested this in below 2 version of swift
# swift --version
swift 2.4.0
# swift --version
python-swiftclient 2.6.0