Confusing Radio Buttons

Can anyone tell me why the radio buttons seem to disappear when a pack size is selected? If I add to cart the product is added but I can see that this will get confusing for customers!

http://www.jacksonsnurseries.co.uk/prunus-laurocerasus-rotundifolia-b-r-test.html

At first make sure that option exceptions and combinations are set correctly for this product