Sorry, but the best answer seems to be: avoid cmd.exe as a shell.

Raku seems to attempt to compensate the shortcomings of cmd, but this can never fully succeed, since cmd does it's own expansions

for instance environment vars inside % are expanded, no matter if quoted or not

D:\tmp\pm>perl -e"print '%OS%'"
Windows_NT
D:\tmp\pm>
[download]

And even if Raku succeeds in better compensating cmd-shell, I sincerely hope this is not globally so on Win and deactivated for other SHELLs.