Hi Tran,
I think I have found a mistake in the Metabox Group plugin. Last month you built in a function to limit the maximum number of clones When adding this goes well. After adding you can add an infinite number of clones. If they are then removed again, the button will disappear too.
Here's my group configuration
id' => PREFIX .'home_usp',
'clone' => true,
'max_clone' => 3,
'type' => 'group',
'fields' => array(