Update (this is why):

Looking inside IPC/Run.pm, the harness sub has the following:

my @args ;

   if ( @_ == 1 && ! ref $_[0] ) {
      if ( Win32_MODE ) {
         @args = ( [ qw( command /c ), win32_parse_cmd_line $_[0] ] ) 
+;
      }
      else {
         @args = ( [ qw( sh -c ), @_ ] ) ;
      }
   }
   elsif ( @_ > 1 && ! grep ref $_, @_ ) {
      @args = ( [ @_ ] ) ;
   }
   else {
      @args = @_ ;
   }
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Thus, the following:

use IPC::Run qw(run harness);
# This will work
my $h = harness "perl", "-v";
run $h;
print "\n\n-------------------\n";
print "Calling harness with one arg...";
print "\n-------------------\n\n";
#This will not work if you don't have command.com
my $h2 = harness "perl -v";
run $h2;
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