product options & checkbox issue

I have a product that I am adding product options to. I am selecting checkbox as the type - so I added 5 checkboxes - all nice and easy from the admin - go to product page - only the first one is checkable - the other 4 can not be checked until the first - seems odd - so looking at the code of the others I see they are disabled:

Any ideas on this one guys?


Change Options type from Sequential to Simultaneous

Thanks Joe excellent