Nodequeue duplicate nodes if add node twice or more

Created a simple nodequeue with the following parameters:

• Queue size: 4
• Reverse in admin view: Enabled

Added 4 different nodes into this nodequeue. Everything is ok at this step.
Next, trying to add the node that already exists in this nodequeue.

The following events take place:

• node at first position is deleted
• node which is currently being added, is stored twice into DB

All this is quite bad, because finally it results in currupted nodequeue, that contains only 3 nodes instead of 4 (the 1-st item is lost).

I have an idea about how to fix this: we need to deny addition of nodes that already exist in nodequeue.
In particular, in autocomplete select we should not display those nodes, that were already added into the nodequeue.

I made the following patch to accomplish this (need to add code to nodequeue_api_autocomplete() function):

  // Select nodes wich added to current nodequeue.
  $exclude = array();
  foreach (_nodequeue_dragdrop_get_nodes($queue, $subqueue) as $queue_node) {
    $exclude[] = $queue_node->nid;
  }
 
  // Add query condition with exclude nids if nodequeue not empty.
  if (count($exclude)) {
    array_unique($exclude);
    $query->condition('n.nid', $exclude, 'NOT IN');
  }

See attached file nodequeue_exclude_dublicates.patch