Push object to an array of Mixed fields in Mongoose

I'm unable to push regular objects to an array of Mixed fields in mongoose.

I'm trying this:

ME.update({_id: eventid},
          {$push: { rawdata: {x: packet.x, y: packet.y} }},
          {upsert:true}, function(err, data) {  
            console.log(err);
            }
    });

However, this only results in an array of ids in the mongodb database:

[rawdata] => Array (
[0] => Array (
    [_id] => MongoId Object (
        [$id] => 50f476a13ebe522960000005
    )
)
[1] => Array (
    [_id] => MongoId Object (
        [$id] => 50f476a13ebe522960000006
    )
)
[2] => Array (
    [_id] => MongoId Object (
        [$id] => 50f476a23ebe522960000007
    )
)
[3] => Array (
    [_id] => MongoId Object (
        [$id] => 50f476a23ebe522960000008
    )
)
[4] => Array (
    [_id] => MongoId Object (
        [$id] => 50f476a23ebe522960000009
    )
)
[5] => Array (
    [_id] => MongoId Object (
        [$id] => 50f476a33ebe52296000000a
    )
)
[6] => Array (
    [_id] => MongoId Object (
        [$id] => 50f476a33ebe52296000000b
    )
)
[7] => Array (
    [_id] => MongoId Object (
        [$id] => 50f476a33ebe52296000000c
    )
)

Not at all what I expected. What's going wrong?

First I create the "rawdata" schema: (Here I use an empty object literal, I also used the Schema.Types.Mixed one)

{ rawdata: { type: {} } }

And then I add that to the bigger schema, which results in something like:

rawdata: 
[ { paths: [Object],
   subpaths: {},
   virtuals: [Object],
   nested: {},
   inherits: {},
   callQueue: [],
   _indexes: [],
   methods: {},
   statics: {},
   tree: [Object],
   _requiredpaths: undefined,
   options: [Object] } ],