validation of radio button group in formbuilder

[the.star]

hi all

after my seventh cmsms website, I'm having an issue with formbuilder and its validation of radio buttons, which doesn't work.
I can tickle the radio button group as "required", but on the frontend the user is able to submit the form, without any radio button selected. Can somebody tell me why? Is this a common issue, I just haven't found anything on the forum?

thanks you all in advance.


cheers

sam