Hi,
If you use "Generic Child Variant" custom fields and if you define different pictures for child products, then it is normal if the pictures get refreshed upon changing the custom field (if you don't define any picture for child-product, the parent product's picture will be used for all child-products). It is a good thing, and i am seeing it works just fine on your website.
Did you already fix the problem? Or do you still somehow experience a problem of image disappearing? (i didn't see any image disappear problem on your website)
Regards