Saving via ProductRepository changes untouched attributes

[ochnygosch]

Saving a loaded product via the ProductRepository updates attribute values of unchanged attributes. Even loading a product and saving it without making changes can lead to a product no longer using default values for a store.

Preconditions

1. Magento 2.1.3
2. Single store mode is disabled

Steps to reproduce

1. Create a simple product
2. Make sure this product uses default value for product name (or other attributes) for default store
3. Load product in a backend controller via getById($productId) method of ProductRepositoryInterface
4. Save the loaded product via save($product) method of ProductRepositoryInterface

Expected result

1. No attribute value of the product should have changed. Especially the product name in store 1 should still use the default value

Actual result

1. The name of the save product is copied from store 0 to store 1 and store 1 no longer uses the default value for the product name

Attached is a sample module that provides a backend controller that loads product with id 1 and saves it without changing an attribute.
ProductSave.zip

[ochnygosch]

I think something in the eav system is seriously broken.

I've tried adding another website with a store and store view (say having the id 2).

Having a product (with id 1) and the following values:

Store 0 Name: "Testproduct"
Store 1 Name: Use default value
Store 2 Name: Use default value

Store 0 Description: "Test description"
Store 1 Description: Use default value
Store 2 Description: "Test description in store 2"

Then I tried to edit an attribute of the new store with the following code:

$product = $this->_productRepository->getById(1,true,2);
$product->setName('Testproduct in store 2');
$this->_productRepository->save($product);

I expected this result:

Store 0 Name: "Testproduct"
Store 1 Name: Use default value
Store 2 Name: Use default value

Store 0 Description: "Test description"
Store 1 Description: Use default value
Store 2 Description: "Test description in store 2"

But I got this result:

Store 0 Name: "Testproduct"
Store 1 Name: "Testproduct in Store 2"
Store 2 Name: Use default value

Store 0 Description: "Test description"
Store 1 Description: "Test description in store 2"
Store 2 Description: "Test description in store 2"

And every other attribute in store 1 got copied from store 2.

[magento-engcom-team]

Possible duplicate #7720