The problem isn't with wantarry, it's something more low level then that, observe a slightly modified version that doesn't use wantarray...

use overload '*' => sub {
    my $div = int(${$_[0]} / ${$_[1]});
    my $mod = ${$_[0]} % ${$_[1]};
    return ($div, $mod);
};
[download]

This still generates "30" for 90/30, regardless of context ... it's as if overloaded operators are allways called in some sort of bizarro scalar context where lists are evaluated as their last element instead of their length...

package mod;
use strict;
use overload '*' => sub {
    return ('yakko', 'wakko', 'dot');
};
sub new {
   my ($class,$val) = @_;
   return bless \$val, $class;
}
package main;
use strict;
my $i = mod->new(90);
my $j = mod->new(60);

my @x = $i * $j;
my $x = $i * $j;
print "@x\n";
print "$x\n";
__END__
dot
dot
[download]

Update: My bad, I totally spaced out on the fact that lists in scalar context evaluate to the last element... i was thinking of it just like an array.