Crossposted from p5p :

This reduces to :

use strict;
use warnings;

sub foo {
 if (1) {
  return do {
   1;
  }
 }
}
sub bar {
 if (1) {
  return do {
   my $x;
   1;
  }
 }
}
sub baz {
 if (1) {
  return scalar do {
   my $x;
   1;
  }
 }
}

my $x = foo;
my $y = bar;
my $z = baz;

print "#$x#\n";
print "#$y#\n";
print "#$z#\n";
[download]

This looks like a duplicate of "my" old bug #38809. If you turn warnings on, you'll notice that bar returns undef. This seems to have to do with the return context, since changing to return scalar do fixes the problem.

Edit: When ran into taint mode, foo fails too.

Edit^2: Bah, exactly what kyle said !