I am testing VM 3.4.5 10057. I found that when you load a product image (second image and more), the setting changes from "reload" to "replace". This is probably undesirable.
(https://i.postimg.cc/9rNSV7Nq/test.png) (https://postimg.cc/9rNSV7Nq)
Just checked with VirtueMart 3.4.5 10071. That one works correctly here. After uploading a second image, it checkbox changes to 'None' (default).