in reply to system command erroneously states 'can't spawn <executable>'
The issue, and the error message, aren't from DOS, they're from Perl source code in win32.c. If the system returns a negative error code, the Perl C code spits out that warning, and sets $? to 255 * 256, which you bit shift down to 255.
I don't know how (yet) to raise a bug issue with the Perl source, but perhaps that error can be checked for which version of the windows perl is running on, and only return it for Windows OSs that don't support negative error codes.