Yeah, it's a version thing:

c:\@Work\Perl\monks>perl -wMstrict -le
"print qq{perl version: $]};
 ;;
 F('hi', 'every', 'body');
 ;;
 sub F {
   my (my $x, my $y, my $z) = @_;
   print qq{\U$x $y $z};
   }
"
perl version: 5.014004
HI EVERY BODY
[download]

I get the same back to 5.8.9.