Return from sort block gives "Use of uninitialized value in sort" warning, but only with explicit return

I'm getting a strange behavior from Perl when I try to return from my sort() block:

#!/usr/bin/perl
use strict;
use warnings;

my @data = sort {
    return &special_sort;
} qw/ 6 1 2 /;

use Data::Dumper;
print STDERR Data::Dumper->Dump([\@data]);

sub special_sort {
    # (imagine some custom sorting logic here)
    return $a <=> $b;
}

This gives the following messages:

Use of uninitialized value in sort at ./mcve.pl line 6.
Use of uninitialized value in sort at ./mcve.pl line 6.
Use of uninitialized value in sort at ./mcve.pl line 6.
$VAR1 = [
          6,
          1,
          2
        ];

As you can see, it also failed to sort the list. The odd thing is, the following sort clauses work without any warnings, and sort the data properly:

my @data = sort {
    &special_sort;
} qw/ 6 1 2 /;

my @data = sort {
    my $res = &special_sort;
    return $res;
} qw/ 6 1 2 /;

my @data = sort {
    return $a <=> $b;
} qw/ 6 1 2 /;

my @data = sort {
    eval { return &special_sort; }
} qw/ 6 1 2 /;

Question 0

What's going on here? Why do those four work, but the first example doesn't? It shouldn't be the return statement causing undefined behavior, since two of the working ones have that.

Question 1

If it turns out the world isn't perfect and I can't (or shouldn't) return from a block, is there an elegant way to effectively do that?

Edit: It was a bug in Perl. (Note: I did some checking, and I'm slowly figuring out this is down to my confusion between how Perl handles BLOCKs vs. SUBs, hence Question 1. The question is still interesting IMO, and confusing behavior on Perl's part.)

For clarity, I'm using Perl 5.32.0.