The url changes to the url of the last product in the bundle. I've confirmed this by observing the behavior then adding an additional product to the bundle. The url then changes to that new product's url. Also, if you change the order of the products, it always changes the url to the last product.
When I load this page ...
https://muifchjkct-staging.onrocket.site/product/bundle-2/
The url changes to the url of the last product in the bundle. I've confirmed this by observing the behavior then adding an additional product to the bundle. The url then changes to that new product's url. Also, if you change the order of the products, it always changes the url to the last product.