Sorting has no effect when a relation has same class than the model

[olivierbaudouin]

Steps to reproduce:

1. In users migration table:
   $table->foreignId('manager_id')->nullable()->constrained('users');

2. In User model:
   public function manager(): BelongsTo
   {
   return $this->belongsTo(User::class, 'manager_id')->select('id', 'fullname');
   }

3. Purity sorting string : 'group.name:asc' -> no effect

All other sorting types on relation are working.

I tried with another Model (Customer that belongs to a group where group is a Customer), and this is the same problem.