Geo: Geohash_cell produces bad neighbors

[clintongormley]

GET /_validate/query?explain
{
  "query": {
    "filtered": {
      "filter": {
        "geohash_cell": {
          "location": {
            "lat": 51.521568,
            "lon": -0.141257
          },
          "precision": "100km",
          "neighbors": true
        }
      }
    }
  }
}

Returns geohashes:

• ebzs - see http://geohash.2ch.to/ebzs
• ebzu - see http://geohash.2ch.to/ebzu
• gcpt - see http://geohash.2ch.to/gcpt
• gcpv - see http://geohash.2ch.to/gcpv
• s0bh - see http://geohash.2ch.to/s0bh
• u10j - see http://geohash.2ch.to/u10j

Only gcpt, gpcv, and u10j are in the right place. The others are in the Gulf of Guinea.