I must admit I am not too hot on closures either but another interesting observation is that making @o global appears to cure the problem.

Then perhaps instead of @::o = () you may want to use our in conjunction with local:

#!/usr/bin/perl

use strict;
use warnings;

sub foo {
    my $window = "a b X20 c X5 d e X17 X12";
    local our @o;
    my @m = $window =~ m/(X\d+(?{push @o, pos}))/g;
    print "Matches: @m,\n";
    print "Offsets: @o,\n\n";
}

foo;
foo;
foo;

__END__

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In reply to Re^3: Multiple uses of (?{ code }) do not appear to be called by blazar
in thread Multiple uses of (?{ code }) do not appear to be called by bsdz

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