On one machine I have, chmod g+s fails to set the sticky bit. The 
command does not return any error, but ls -l continues to show the bit 
not set.

    $ mkdir foo
    $ chgrp flight foo
    $ chmod g+ws foo
    $ ls -ld foo
    drwxrwxr-x+ 1 nort flight 0 Jun 29 06:50 foo

I ran strace, and it looks like the correct system call parameter is 
getting passed.

I am curious as to how the sticky bit is implemented. It isn't obvious 
what underlying Windows functionality (if any) is applied. Ah, just 
checked on a system where this works, and creating a file in the 
directory from the command shell does not set the group, so presumably 
this functionality is all within cygwin. That works for my application, 
except when it doesn't.

Any suggestions on what I should look for?