TYPO3 Core

I have the follwowing TCA configuration

'config' => [
    'type' => 'datetime',
    'format' => 'date',
    'default' => 0,
    'behaviour' => [
        'allowLanguageSynchronization' => true,
    ],
],

When I now select "Today" from the date picker, the current date is displayed. But when I save the form, the field is empty again.

I encountered this also on a datetime field (with time displayed). The current time is not stored, but when I date back 2 hours the date and time is stored correctly. The server is running on UTC, maybe this explains the difference.