TYPO3 Core

When your TCA has such definition:

        'rulesets' => array(
            'label' => 'LLL:EXT:image_autoresize/Resources/Private/Language/locallang_tca.xlf:tx_imageautoresize.rulesets',
            'config' => array(
                'type' => 'flex',
                'ds_pointerField' => 'list_type',
                'ds' => array(
                    'default' => 'FILE:EXT:image_autoresize/Configuration/FlexForms/Rulesets.xml',
                ),
            ),
        ),

FormEngine is properly showing the container and everything seems to work properly (add/delete/move):

However the validation on fields of the child form (input text, max length, ...) is not invoked right after adding a new child (this is the first bug, not that bad at first sight) but the transfer from form fields to corresponding hidden fields does not happen either, making the submitted form totally empty on save, showing an empty child on reload and only then "working" as expecting.

To easily reproduce/debug, just install EXT:image_autoresize (from git repository) and apply https://review.typo3.org/#/c/44062, then go to EM and click on the title to configure the extension, under "Rule Sets" (last tab), you see such a definition of FlexForm-based record.

I tried the same with a standard TCA (not "hacking" for standalone FormEngine) and the problem is the same, so it's not related to standalone FormEngine.