is this a lexicals bug?

$ cat /tmp/test
class M {
    has M @.ms is rw;
    method s($i=0) {
        $i ~ "[{ map { "{$_.s($i + 1)}" }, self.ms }]"
    }
}

my $m = M.new;
my $m2 = M.new;
$m2.ms = M.new;
$m.ms = M.new, $m2, M.new;
say $m.s;

$ perl6 /tmp/test
0[1[] 2[3[]] 4[]]

# expected output:
# 0[1[] 1[2[]] 1[]]

# This used to be code doing indentation before I golfed it. The numbers correspond
# to nesting level.