Updating a document resets reference strength

[TedSanne]

When querying a document all references seem to have the Weak prop on SanityReference set to null.
This in turn seems to be converted into a strong reference when the document is updated.

Example:

var docSet = await _sanity.DocumentSet<Filmomtale>()
                .Include(f => f.Distributor)
            .Where(f => f.Id == id)
            .ExecuteAsync(cancellationToken);

var doc = docSet.Single();

<... update some fields on doc, but leave Distributor reference untouched ....>

await _sanity.DocumentSet<Filmomtale>()
                    .Update(doc)
                    .CommitAsync(cancellationToken: cancellationToken);

Here "Distributor" is a reference to another document type, the schema specifies the reference as weak:

{
			title: 'Distributør',
			name: 'distributor',
			type: 'reference',
			readOnly: false,
			to: [
				{ type: 'distributor' }
			],
			weak: true,
			group: "metadata"
		}

When debugging this I can see that the Weak property on the reference to Distributor is null.
After the document has been updated, Sanity Studio now shows a warning "Reference strength mismatch" for the Distributor field.

Is this a bug, or is there something else I need to do when querying to make sure the reference is returned?

EDIT: I am using 1.5.0 from NuGet

[TedSanne]

Other weak references that are not .Incude(...) in the query are not affected.