TYPO3 Core

My slug field is

        'slug' => [
            'exclude' => true,
            'label' => 'LLL:EXT:core/Resources/Private/Language/locallang_tca.xlf:pages.slug',
            'config' => [
                'type' => 'slug',
                'size' => 50,
                'generatorOptions' => [
                    'fields' => [
                        'title', 'first_name', 'last_name'
                    ],
                    'fieldSeparator' => '-'
                ],
                'fallbackCharacter' => '-',
                'eval' => 'unique',
                'default' => ''
            ]
        ],

The fields first_name and last_name are normal input fields. The field title is a select field.

When i use the slug refresh button, then the slug includes the first_name and last_name only. (Wrong)

When i empty the slug field and save the record, then the slug includes all 3 field values (Ok)