date-picker: localized date incorrectly submitted as part of

I am trying to use duet-date-picker with Thymeleaf (server-side rendering). It works as long as I don’t use the localization support.

I added this in a <script> tag in my page:

    const picker = document.querySelector('duet-date-picker');
    const DATE_FORMAT = /^(\d{1,2})\.(\d{1,2})\.(\d{4})$/;

    if (picker) {
        picker.dateAdapter = {
            parse(value = '', createDate) {
                try {
                    console.log('parsing' + value);
                    const matches = value.match(DATE_FORMAT);

                    if (matches) {
                        return createDate(matches[3], matches[2], matches[1]);
                    }
                } catch (err) {
                    console.log(err);
                }
            },
            format(date) {
                console.log('formatting: ' + date);
                return `${date.getDate()}.${date.getMonth() + 1}.${date.getFullYear()}`;
            },
        };
    }

I see lot’s of formatting... statements, but never parsing... and also no error in the console.

When I check with dev tools, I see updates to the value attribute of <duet-date-picker>, but the value of the actual <input> is not updated. Due to this, my server-side thinks that nothing was selected. For some reason, that does not seem to be an issue when not using the localization support. Am I doing something wrong?