clone_empty_start bug?

Hello,
Since version 5.10 and still existing in 5.10.2, I have problems with clonable group containing a select field.
Not sure if it's related to the new clone_empty_start feature, but everytime I edit my block, a new empty block is automatically added at first position, I can't delete it.
If the group does not contains a select, or if changed to select_advanced, it works correctly...

Minimal code to reproduce:

$meta_boxes[] = [
	'title'           => 'CTA Info',
	'id'              => 'cta-info',
	'type'            => 'block',
	'context'         => 'side',
	'render_template' => get_stylesheet_directory() . '/blocks/campagnes-new/cta-info/template.php',
	'fields'          => [
		[
			'id'   => 'ctas',
			'name' => 'CTA',
			'type' => 'group',
			'clone' => true,
			'sort_clone' => true,
			'clone_empty_start' => false,  // true has same effect
			'fields'      => [
				[
					'type' => 'select',
					'id'   => 'type_cta',
					'name' => 'Type',
					'options' => [
						'phone'  	  => 'Phone',
						'email' 	  => 'Email',
					],
				],
				[
					'type' => 'text',
					'id'   => 'title',
					'name' => 'Title',
				]
			],
		],
	],
];