Bug with bindings on union with joins

In Laravel 4.2 there is a bug that when you perform a union on queries that have bindings in the joins, the join bindings do not get merged. 4.2 not being supported, they won't accept/fix this. I've gone through the Builder and Grammar and I'm not finding where the problem is. I will be doing a lot of queries with unions that contain joins so I would like to fix this in my framework instead of working around this. Anyone able to help me identify how to fix this in the Builder or Grammar?

Example code: https://paste.laravel.io/r5VQ1

  public function test2()
  {
    $param1 = 1;
    $param2 = 2;

    $tableA = \DB::table('childA')
        ->select(['*'])
        ->leftJoin('inventory', function($join) use ($param1) {
          $join->where('inventory.tenantId', '=', $param1);
        });

    $tableB = \DB::table('childB')
        ->select(['*'])
        ->leftJoin('inventory', function($join) use ($param2) {
          $join->where('inventory.tenantId', '=', $param2);
        });

    $tableA->union($tableB)
      ->orderBy('code');

    $sql = $tableA->toSql();
    $bindings = $tableA->getBindings();

    $this->assertEquals(array(1, 2), $bindings);

    // $bindings = array(1), should be array(1, 2)

  }

via user3720435