Laravel 5.1.* Custom Pivot Class Array Not Casted - mysql

Question

I have a Model called User and another Model called Roles and they are linked with each other through a belongsToMany relationship. But I needed to cast certain pivot attributes so I used a custom pivot class RoleUserPivot which basically looks like follows:
...
use Illuminate\Database\Eloquent\Relations\Pivot;
class RoleUserPivot extends Pivot
{
protected $casts = [
'active' => 'boolean',
'permissions' => 'array',
];
}
...
The relationship definition in User and Role models is as follows:
...
// User Model
public function roles()
{
return $this
->belongsToMany('App\Role')
->withPivot(
'active',
'permissions'
);
}
public function newPivot(Model $parent, array $attributes, $table, $exists)
{
if ($parent instanceof Role) {
return new RoleUserPivot($parent, $attributes, $table, $exists);
}
return parent::newPivot($parent, $attributes, $table, $exists);
}
...
And similarly:
...
// Role Model
public function users()
{
return $this
->belongsToMany('App\User')
->withPivot(
'active',
'permissions'
);
}
public function newPivot(Model $parent, array $attributes, $table, $exists)
{
if ($parent instanceof User) {
return new RoleUserPivot($parent, $attributes, $table, $exists);
}
return parent::newPivot($parent, $attributes, $table, $exists);
}
...
The problem I am having is, while the active field is properly cast to boolean, the permissions field is not cast to array, instead the same string in the database is returned. I assure that the pivot table is properly setup and permissions column is MySQL TEXT column.
Currently I am using Laravel 5.1.16 (LTS).