Native driver find from Mongoose model not returning Cursor

I'm trying to execute a native MongoDB find query via the collection property of a Mongoose Model. I'm not supplying a callback so I expect the find to return a Cursor object, but it returns undefined instead. According to the Mongoose docs, the driver being used is accessible via YourModel.collection and if I switch to purely using the native driver code find does return a Cursor so I can't figure out what's going on.

Here's a code snippet that reproduces the problem:

var db = mongoose.connect('localhost', 'test');
var userSchema = new Schema({
    username: String,
    emailAddress: String
});
var User = mongoose.model('user', userSchema);

var cursor = User.collection.find({});
// cursor will be set to undefined

I've tried to step into the code with node-inspector, but it's not letting me. Any idea what I'm doing wrong?