Otherwise, the variable is
       implicitly local to the loop and regains its former value upon exiting
       the loop.  If the variable was previously declared with "my", it uses
       that variable instead of the global one, but it’s still localized to
       the loop. 

If you also check the references you will see that the '$i' are pointing to different locations.

use strict;
use warnings;
$,=",";
$\="\n";

my $i = 6;
sub my_print {
  print $i,\$i;
}
;

for $i (qw|x y|) {
  my_print();          
  print " (Perl Style:\$i==$i)",\$i,"\n";
}
[download]

6, SCALAR(0x8fa4e38)
 (Perl Style:$i==x), SCALAR(0x8f86760), 

6, SCALAR(0x8fa4e38)
 (Perl Style:$i==y), SCALAR(0x8fa4da8), 
[download]

That's why PBP says to always use lexical loop vars in foreach!