TYPO3 Core

I can confirm this problem on Typo3 8.7.4 LTE

A dirty quick fix:

File: sysext\backend\Classes\Controller\Wizard\AddController.php
Method: main

SEARCH:

$currentValue = $currentParentRow[$this->P['field']];
if (is_array($currentValue)) {
    $currentValue = implode(',', array_column($currentValue, 'uid'));
}

REPLACE:

$currentValue = $currentParentRow[$this->P['field']];
if (is_array($currentValue)) {

  $arrayToImplode = array_column($currentValue, 'uid');

  if(count($arrayToImplode) == 0 && count($currentParentRow[$this->P['field']]) > 0) {
    $arrayToImplode = $currentValue;
    foreach($arrayToImplode as $key => $elementId) {
      if(!is_array($elementId) && !is_object($elementId))
      $arrayToImplode[$key] = $this->table . '_' . $elementId;
    }
  }
  $currentValue = implode(',', $arrayToImplode);
}

I think, there is also a conceptual problem:
A wizard controller should not be able to modify a relationship as much as it is implemented here - especially it should not be necessary to convert an array to a string and back.

Thank you for your response, Fabian.

We'll see what we can do.

FYI: I added the hotfix by Fabian to the extension I wrote earlier in https://forge.typo3.org/issues/76863#note-5 for this project of mine, but I was unable to replicate the problem, so this is just a shot into the blue I must admit.
Could someone post a reproducible test case for this?

The updated add_wizard hotfix extension can be found on github and packagist:
https://packagist.org/packages/kevinditscheid/add-wizard

Patch set 2 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55779

Patch set 3 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55779

Solved in #82461 please close