Running an "unset" on a key inside of array objects says it updated documents but it didn't.

Example doc:

{
        "_id" : ObjectId("52c5e5d2bd546795dee87ca4"),
        "c" : [
                {"pi" : NumberLong(2368999)},
                {"pi" : NumberLong(2368999)},
                {"pi" : NumberLong(2368999)}
        ]
}

Example query:

db.example.update({_id: ObjectId("52c5e5d2bd546795dee87ca4")}, {$unset: {"c.pi": 1}})

When I run that query using the PHP driver it returns:
"updatedExisting"= > true
"n" => 1

However nothing was actually unset. I know there's another bug filed (SERVER-1243) for a feature request to use a position operator on multiple items, but this should have affected ALL items in the collection, I'm not using $elemMatch or anything else. Is that not supported?

I said affects versions 2.2.3 because that's all we have running at Grooveshark but it might affect newer versions.