> db.test5.ensureIndex(

{x:"foo"}

)
> db.test5.getIndexes()
[
{
"name" : "id",
"ns" : "test.test5",
"key" :

{ "_id" : 1 }

},
{
"_id" : ObjectId("4d46194d53ffe3441923319f"),
"ns" : "test.test5",
"key" :

{ "x" : "foo" }

,
"name" : "x_",
"v" : 0
}
]

It seems like it should be 1 of the 3 possible values when it is stored.