Server: running on a single local server node (mongod)

To benchmark the geospatial indexing, I generated a collection containing 9M elements. The element contains randomly generated geo-coordinates (lat/long).
The collection structure is pretty simple:
> db.Content.find({},

{location:1}

).limit(2)
{ "_id" : ObjectId("4c64edf60353f7d9181e21aa"), "location" :

{ "lat" : -38.03453826904297, "lon" : -141.4888458251953, "alt" : 0 }

}
{ "_id" : ObjectId("4c64edf60353f7d90f1e21aa"), "location" :

{ "lat" : -21.978824615478516, "lon" : -151.79954528808594, "alt" : 0 }

}
> db.Content.find().count()
9000000
> db.system.indexes.find()
{ "name" : "id", "ns" : "mrs.Content", "key" :

{ "_id" : 1 }

}
>

The error happens when issuing the indexing command at the shell:
> db.Content.ensureIndex(

{location:"2d"}

)
in > 0
The log says:
Fri Aug 13 01:53:21 [initandlisten] connection accepted from 127.0.0.1:54010 #16
Fri Aug 13 01:53:32 [conn16] building new index on

{ location: "2d" }

for mrs.Content
Fri Aug 13 01:53:32 [conn16] Buildindex mrs.Content idxNo:1 { _id: ObjectId('4c65080cd89977e27aa968f0'), ns: "mrs.Content", key:

{ location: "2d" }

, name: "location_" }
Fri Aug 13 01:54:15 [conn16] mrs.system.indexes Assertion failure in > 0 db/geo/2d.cpp 199
Fri Aug 13 01:54:16 [conn16] Caught Assertion in insert , continuing
Fri Aug 13 01:54:16 [conn16] insert mrs.system.indexes exception 0 assertion db/geo/2d.cpp:199 43983ms