Stack frames in the CV->PADLIST? $f isn't in something I'd immediately recognize as living in PADLIST but perhaps it is in a temporary. PadWalker would show it, I'll bet.

UPDATED. It'd be possible to remove those RV to the self-CV and decrement their reference count.

use B 'svref_2object';
package B::SV;
use overload '""' => sub {
    my ( $self ) = @_;
    return sprintf '%s=(%x)', ref $self, $$self;
};
package main;

sub padinfo {
    my $cv = svref_2object( $_[0] );
    my $cvdepth = $cv->DEPTH;
    my ( $namesav, @stackav ) = $cv->PADLIST->ARRAY;
    my @names = map { $_->can('PV') ? $_->PV : undef } $namesav->ARRAY
+;
    my @stack_ref = map [ $_->ARRAY ], @stackav;

    print STDERR "$_[0]\n";
    for my $depth ( 0 .. $#stack_ref ) {
        if ( $depth == $DEPTH ) {
            print STDERR '-' x 32;
            print STDERR "LEVELS FOLLOWING MAY BE REAPED\n";
        }
        print STDERR "  $depth\n";
        for my $ix ( 0 .. $#{ $stack_ref[$depth] } ) {
            next unless defined $names[$ix];
            print STDERR "    $names[$ix]: $stack_ref[$depth][$ix]\n";
            print STDERR '        REFCNT:'. $stack_ref[$depth][$ix]->R
+EFCNT."\n";
            if ( $stack_ref[$depth][$ix]->can( 'RV' ) ) {
                print STDERR '            '.$stack_ref[$depth][$ix]->R
+V."\n";
                print STDERR '            REFCNT:'.$stack_ref[$depth][
+$ix]->RV->REFCNT."\n";
            }
        }
    }
}

sub refcnt {
    print STDERR svref_2object( $_[0] )->REFCNT . "\n";
}

my $f;
$f = sub { my $g = time; $f->( $_[0] - 1 ) if $_[0] >= 0 };

refcnt $f;
refcnt \ $f;
padinfo $f;
$f->(1);
refcnt $f;
refcnt \i $f;
padinfo $f;
[download]

PRODUCES

1 # $f
3 # \$f
CODE(0x812a180)
--------------------------------LEVELS FOLLOWING MAY BE REAPED
  0
    $g: B::NULL=(81b6818)
        REFCNT:1
    $f: B::RV=(812aac8)
        REFCNT:2
            B::CV=(812a180)
            REFCNT:1
1 # $f
5 # \$f
CODE(0x812a180)
--------------------------------LEVELS FOLLOWING MAY BE REAPED
  0
    $g: B::IV=(81b6818)
        REFCNT:1
    $f: B::RV=(812aac8)
        REFCNT:4
            B::CV=(812a180)
            REFCNT:1
  1
    $g: B::IV=(81abe14)
        REFCNT:1
    $f: B::RV=(812aac8)
        REFCNT:4
            B::CV=(812a180)
            REFCNT:1
  2
    $g: B::IV=(81abb98)
        REFCNT:1
    $f: B::RV=(812aac8)
        REFCNT:4
            B::CV=(812a180)
            REFCNT:1
[download]