Custom pivot's mutator called when getting belongsToMany() relationship

[ghost]

• Laravel Version: 5.5.34
• PHP Version: 7.0.22
• Database Driver & Version: MySQL 5.7.20

Description:

Getting or eager-loading a belongsToMany() relationship causes any defined custom pivot's mutators to be called.

Steps To Reproduce:

Create two simple models with a custom pivot that has a mutator:

class OneTable extends Model
{
    public $table = 'one_table';

    protected $guarded = [];

    public function anotherTables()
    {
        return $this->belongsToMany(AnotherTable::class, 'one_table2another_table', 'one_table_id', 'another_table_id')
            ->withPivot('data')
            ->using(OneTable2AnotherTable::class);
    }
}

class AnotherTable extends Model
{
    public $table = 'another_table';

    protected $guarded = [];
}

class OneTable2AnotherTable extends Pivot
{
    public function setDataAttribute($value)
    {
        throw new \Exception('MUTATOR CALLED');
    }
}

Get a OneTable instance and its related AnotherTables:

$oneTable = OneTable::find(1);
$oneTable->anotherTables()->get();

Or eager-load its related AnotherTables:

OneTable::with('anotherTables')->find(1);

In both cases, the OneTable2AnotherTable pivot's mutator is called and the respective exception is therefore thrown.
Note that this doesn't happen when getting a regular non-pivot model or a regular model's related models defined via hasMany().