> The value of exit returned to the parent should be status & 0377.

Apparently, this is not so on Windows.  See msg241903 in #24045.

POSIX defines [1] exit to return status & 0377, but that does not mean that sys.exit(256) must return 0 without a warning.  It is very unlikely that someone would intentionally use code=256 to signify success.  It is much more likely that sys.exit(256) is a result of a programming error.

I believe a better behavior for sys.exit() would be to truncate the code values to 8-bit range so that non-zero status would always be returned as non-zero, but possibly different value.

[1] http://pubs.opengroup.org/onlinepubs/009695399/functions/exit.html