Keep a checkbox checked on large product view with grouping

[rbrtsluk]

hi I have this problem with my checked checkbox on my large product view. I've used JS and all is working fine but when I group products and I select anything in the drop down other than the default the product view breaks and the checkbox becomes unchecked.

here is the site iv'e currently been working on for a long time!!

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Beyonce - Midnight Blue

any help would be greatly appreciated

thanks luke