Which versions of perl/Win32::API are you using?

I cannot reproduce your problem using AS811(5.8.6)/0.41

C:\test>junk a
string[18] = 'perl -x -S junk a '

C:\test>junk a b c d e f g h
string[32] = 'perl -x -S junk a b c d e f g h '

C:\test>type junk.bat
@rem = '--*-Perl-*--
@echo off
if "%OS%" == "Windows_NT" goto WinNT
perl -x -S "%0" %1 %2 %3 %4 %5 %6 %7 %8 %9
goto endofperl
:WinNT
perl -x -S %0 %*
if NOT "%COMSPEC%" == "%SystemRoot%\system32\cmd.exe" goto endofperl
if %errorlevel% == 9009 echo You do not have Perl in your PATH.
if errorlevel 1 goto script_failed_so_exit_with_non_zero_val 2>nul
goto endofperl
@rem ';
#!/usr/bin/perl -w
#line 15

use Win32::API;

Win32::API->Import("kernel32", "LPTSTR GetCommandLine()");

my $string = pack("Z*", GetCommandLine());

print "string[".length($string)."] = '$string'\n";

__END__
:endofperl

C:\test>perl -MWin32::API -wle"print $Win32::API::VERSION"
0.41
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