Error cloning Entities

Maybe i found a bug or maybe i made mistake. When i try to clone an entities model dont save unless i fill attributes manually BUT if i make d() i see attributes filled correctly. This is the code:

PHP Code:

$UserModel = model(UserModel::class);

$oldEntry = $UserModel->first();

$newEntry = clone $oldEntry;

$newEntry->id= null;

//name is required and filled in old entry
//unless this it will get an error "name required"
 $newEntry->name = 'ciccio';

$UserModel->insert($newEntry); 


Any Ideas ?