TYPO3 Core

In \TYPO3\CMS\Backend\Form\FormDataProvider\TcaSelectItems there is the following code:

        // For single select fields we just keep the current value because the renderer
        // will take care of showing the "Invalid value" text.
        // For maxitems=1 select fields is is also possible to select empty values.
        // @todo: move handling of invalid values to this data provider.
        if ($fieldConfig['config']['maxitems'] === 1) {
            return array($result['databaseRow'][$fieldName]);
        }

However, that is actually invalid becasue even if I have maxitems === 1 I can still use MM relations like for categories which would then need to be resolved.
We need to check for MM table here.

Furthermore I think this issue is actually related:
https://forge.typo3.org/issues/69836

Becasue that way 0 was returned instead of "parsed" but once an item is stored it would always be "1" as the field only contains the count.