ACF 5.8-Beta-4.1: Conditionally hidden sub field should return empty value instead of default

The case:

Two subfields:

• Arrangement: blocks (default), slides
• Position: before (default), after

A position choice is shown only if "slides" is chosen in the first control (conditional logic).

The issue:

Steps:

1. When I insert a block and don't touch anything, the returned position value is empty. This is valid and expected.
2. But when I click "Slides", even once, go back to "Blocks" and save the page, from that moment the returned position will never be empty. It returns default value "before" instead. I expect that conditionally hidden field will still return empty value.

The code:

/**
 * Test ACF blocks in 5.8-beta4
 */

function my_acf_block_render_callback() {
	$settings = get_field( 'my-settings' );
	echo 'Position: ' . ( ! empty( $settings['position'] ) ? $settings['position'] : 'empty' );
}

add_action( 'acf/init', 'my_acf_blocks_init' );
function my_acf_blocks_init() {
	/**
	 * Register block
	 */
	acf_register_block_type( array(
		'name'            => 'my',
		'title'           => __( 'My Test Block', 'my-acf' ),
		'description'     => __( 'A block for entering a link name and a custom URL.', 'my-acf' ),
		'render_callback' => 'my_acf_block_render_callback',
		'category'        => 'formatting',
		'icon'            => 'external',
		'keywords'        => array(),
		'supports'        => array( 'align' => false ),
		'mode'            => 'edit',
	) );

	/**
	 * Define block fields
	 */
	acf_add_local_field_group( array(
		'key' => "group_my",
		'title' => __( 'Block :: My Test Block', 'my-acf' ),
		'location' => array(
			array(
				array(
					'param' => 'block',
					'operator' => '==',
					'value' => 'acf/my',
				),
			),
		),
		'fields' => array(
			array(
				'key' => "field_my-settings",
				'label' => false,
				'name' => "my-settings",
				'type' => 'group',
				'layout' => 'block',
				'sub_fields' => array(
					/* Arrangement */
					array(
						'key' => "field_my-settings-arrangement",
						'label' => __( 'Arrangement', 'my-acf' ),
						'name' => 'arrangement',
						'type' => 'button_group',
						'choices' => array(
							'blocks' => __( 'Blocks', 'my-acf' ),
							'slides' => __( 'Slides', 'my-acf' ),
						),
						'default_value' => 'blocks',
						'layout' => 'horizontal',
						'wrapper' => array(
							'width' => '50',
						),
					),
					/* Position */
					array(
						'key' => "field_my-settings-position",
						'label' => __( 'Images position', 'my-acf' ),
						'name' => 'position',
						'type' => 'radio',
						'choices' => array(
							'before' => __( 'Before', 'my-acf' ),
							'after' => __( 'After', 'my-acf' ),
						),
						'default_value' => 'before',
						'layout' => 'horizontal',
						'wrapper' => array(
							'width' => '50',
						),
						'conditional_logic' => array(
							array(
								array(
									'field' => "field_my-settings-arrangement",
									'operator' => '==',
									'value' => 'slides',
								),
							),
						),
					),
				),
			), // EOF settings
		),
	) );
}

Start with the PHP reproduction in the issue and repeat the save sequence: leave Blocks selected, switch to Slides, return to Blocks, and save. Trace how the ACF group returns the conditionally hidden position subfield after saving. Done means the position value remains empty when the field is hidden, rather than returning its default value "before".