variation issue

hello

when i have no variations of a product everything works fine, however when there are variations, in this case different show sizes, when you click an out of stock item, nothing happens, but then when you try to add an out of stock item to the basket the page reloads with an error message at the top of the page, and the email when back in stock button shows

then if you select between instock and out of stock the button comes and goes, but for some reason you need to try adding the out of stock on to the basket before this happens, any idea how i can get it to come and go without adding to basket first.

just to make sure you understand, go to the page linked, select a size that is out of stock, then select a size that is in stock, nothing changes

then go to an out of stock size again, and add that to the basket, the page will re load and you will see an error at the top of the screen and the email when back in stock button appears, now select and in stock size, the button goes, select an out of stock size, the button is back, i need it to come and go like this before the first add to basket.

thank you and i am happy to provide and additional information that is needed!

The page I need help with: [log in to see the link]