Another unfortunate bug with references appears to be that statics holding references inside methods are actually transient, and a reference will be lost.

For example, calling the following code several times will initialise $db and return every time with a new instance.

function &getInstance()
  {
    static $db;

    if (!isset($db)) {
      $db =& new FS_DB();
    }

    return $db;
  }

whereas the following will give true singeton behaviour and initialise just once, as expected.

function &getInstance()
  {
    static $db;

    if (!isset($db)) {
      $db = new FS_DB();
    }

    return $db;
  }