Laravel 5.1 Updated Model Relationships when Eager

Question

I'm updating a Rental that belongsTo a Location, and I can fill and persist the Rental data, but when I fill the location relationship data retrieved through eager loading if I try to save(), update(), or push(); It isn't persisted to the database. According to the docs push() should work as it apparently persists relationships.

Update Action

public function update($id, RentalUpdateRequest $request)
{
    // Eager load the rental with relationships
    $Rental = Rental::with('location')->find($id);

    // Retrieve rental data from request, and fill
    $requestData = $request->only('stall', 'level', 'description');
    $Rental->fill($requestData);

    // Retrieve rental location data from request, and fill
    $requestData = $request->only(
        'location.street_address',
        'location.city',
        'location.province',
        'location.country',
        'location.postal_code'
    );
    $Rental->location->fill($requestData);

    // Persist rental to database, as well as all relationships
    $Rental->update();

    // Return rental data for capture by AngularJS interceptor
    return response()->json([
        'rental' => $Rental,
        'action' => 'rental_updated',
        'message' => trans('rental.updated')
    ]);
}

Payload and Eager Loaded Data is Formatted the Same Way

Original rental loaded in the client

rental: 
    description: "This is a rental."
    id: 1
    level: "7"
    location: 
        city: "Victoria"
        country: "Canada"
        id: 11
        postal_code: "V8T 2L5"
        province: "British Columbia"
        street_address: "180 Blanshard Dr."
    region_id: 1
    rental_location_id: 11
    stall: "7"
    user_id: 1

If the Payload is:

rental: 
    description: "This is a rental."
    id: 1
    level: "9" <-- Changed
    location: 
        city: "asdf" <-- Changed
        country: "asdf" <-- Changed
        id: 11
        postal_code: "V8T 2L5"
        province: "asdf" <-- Changed
        street_address: "180 Blanshard Dr."
    region_id: 1
    rental_location_id: 11
    stall: "7"
    user_id: 1

Response after Save(), Update(), or Push()

rental: 
    description: "This is a rental."
    id: 1
    level: "9" <-- Persisted
    location: 
        city: "Victoria" <-- NOT Persisted
        country: "Canada" <-- NOT Persisted
        id: 11
        postal_code: "V8T 2L5"
        province: "British Columbia" <-- NOT Persisted
        street_address: "180 Blanshard Dr."
    region_id: 1
    rental_location_id: 11
    stall: "7"
    user_id: 1

Appears that in Laravel 5.1 push() is being dropped from the API, no longer in 5.1 docs, but save() and update() don't work either, any suggestions?

I've run into this several times now, where I try to set attributes of a eagerly loaded relationship, but only the top level key:value pairs are persisted, and the child relationship pairs are not. The only way around this appears to be to grab the location separately and save(), but what is the point of eager loading like this if I can't save the relationship, and have to make another request to the DB.