title: MongoDB: Too many positional (i.e. '$') elements found in path
body: <p>I just upgraded to Mongo 2.6.1 and one update statement that was working before is not returning an error. The update statement is:</p>
  
  <pre><code>db.post.update( { 'answers.comments.name': 'jeff' },
      { '$set': {
          'answers.$.comments.$.name': 'joe'
      }},
      { multi: true }
  )
  </code></pre>
  
  <p>The error I get is:</p>
  
  <pre><code>WriteResult({
      "nMatched" : 0,
      "nUpserted" : 0,
      "nModified" : 0,
      "writeError" : {
          "code" : 2,
          "errmsg" : "Too many positional (i.e. '$') elements found in path 'answers.$.comments.$.createUsername'"
      }
  })
  </code></pre>
  
  <p>When I update an element just one level deep instead of two (i.e. <code>answers.$.name</code> instead of <code>answers.$.comments.$.name</code>), it works fine. If I downgrade my mongo instance below 2.6, it also  works fine.</p>