TYPO3 Core

TYPO3 8.7.6.: I have a problem with the addRecord-Wizard (fieldControl) in a MN-Relation.

given:
I have defined two relations.

when:
If I press the plus near the selectMulipleSideBySide-Element in the backend, I can create a new record for a new relation.

mistake:
After saving the new record, the new relation to the new record will replace the old two relations.

expected:
After saving the new record, I will see three (= one new + two old) relations.

I testet the option in fieldControl with 'append' and 'prepend' in 'setValue: in TCA
I changed variated multiple to 1

See TCA-example for Relationfield

            'study_programs' => array(
            'exclude' => 1,
            'label' => 'LLL:EXT:... study_programs',
            'config' => array(
                'type' => 'select',
                'renderType' => 'selectMultipleSideBySide',
                'foreign_table' => 'tx_..',
                'MM' => 'tx_...,
...
                'multiple' => 0,
                'fieldControl' => [
                    'editPopup' => [
                        'disabled' => false,
                        'options' => [
                            'title' => 'Edit The selected record!',
                        ],
                    ],
                    'addRecord' => [
                        'disabled' => false,
                        'renderType' => 'addRecord',
                        'options' => [
                            'title' => 'Definiere ',
                            'setValue' => 'append',
                            'pid' => '###CURRENT_PID###',
                        ],
                    ],
                ],
            ),
        ),