That error message should only occur when you run kinit -k without
specifying a client principal name on the command line.
Since you clearly are specifying a principal name, my best guess is
that we introduced an argument parsing bug on Windows when we added
getopt_long() support to the Unix build (in commit
8f9ade8ec50cde1176411085294f85ecfb2820a4 on Feb 24 2016).
Specifically, I suspect the "optind" variable as seen by kinit is not
set correctly after the call to getopt_long().