Checkbox required field

Hi,
there is a problem with required checkboxes as a custom field.
When adding a post and not checking this box you get the array displayed. So it looks like there is no validation or checking for the checkbox before submitting like with the text input fields.
Somebody knows how to fix that?

Thanks 🙂
Phil

http://ww.wp.xz.cn/plugins/wp-user-frontend/