Under what circumstances is "unless" different from "if not"?

I used to think that unless and if not were fully equivalent, but this Q&A made me realize they can result in different output under list context:

use strict;
use warnings;
use Data::Printer;
use feature 'say';

my %subs = (
              unless => sub {
                            my ( $value ) = @_ ;

                            return "$value is a multiple of 3"
                              unless $value % 3 ;
                        },
              if_not => sub {
                            my ( $value ) = @_ ;

                            return "$value is a multiple of 3"
                              if not $value % 3 ;
                        },
           );

for my $name ( keys %subs ) {

    my $sub = $subs{$name};
    say $name;
    my @results = map { $sub->($_) } 1 .. 10;
    p @results;
}

Output

if_not
[
    [0] "",
    [1] "",
    [2] "3 is a multiple of 3",
    [3] "",
    [4] "",
    [5] "6 is a multiple of 3",
    [6] "",
    [7] "",
    [8] "9 is a multiple of 3",
    [9] ""
]
unless
[
    [0] 1,
    [1] 2,
    [2] "3 is a multiple of 3",
    [3] 1,
    [4] 2,
    [5] "6 is a multiple of 3",
    [6] 1,
    [7] 2,
    [8] "9 is a multiple of 3",
    [9] 1
]

The code snippet above shows that unless and if not cause the subroutine to see different values of the last-evaluated expression.

It seems that this is because if not considers not to be part of EXPR, whereas unless doesn't consider it to be part of EXPR.

Question

Are there any other examples of code usage where the two are not quite synonymous?