Note that you can also work around it by declaring a lexical outside the scope of the sub:

{
    my @inserts;
    sub gf
    {
        @inserts = ();
        my $ins1 = '4 A -4 C -4 B 1 D';
        print "\nat the beginning: " . \@inserts . "\n";
        print $ins1, "\n";
        my $re = qr/[\d+-]+(?: \w ([\d+-]+)(?{print \@inserts, "\n"; p
+ush @inserts, $1}))*/;
        $ins1 =~ /$re/g;
        print "\n" . join ' ', @inserts;
    }
}
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You might notice that I created a regex variable. I had hoped that that would cause the regex to be bound at runtime, but no such luck. Creating an empty variable and inserting it in the regex does force runtime evaluation (at least inasmuch as it demands use of use re 'eval'), but it still doesn't make the (?{}) section use the current incarnation of @inserts.