Hey @ah2010,
Based on the translation of that thread, it sounds like the inventory stock is managed at the product level for that variable product (the ‘parent’ or ‘variable product’ level), meaning that the single stock count is added on the “Inventory” tab, like this example, rather than managing the stock individually for each option at the ‘child’ or ‘variation’ level (where the “X” is shown in the screenshot):
https://d.pr/i/Z9ZeTC
If that is correct, the behavior that you described is expected, as the item would need to be removed from the cart in order for a different variation to be selected.
I’m not sure if you already have an option to edit the selection in the cart or not, but I set up a quick product on my test site that was a Simple Product that had a stock count of 1 and product add-ons for the different options available (A, B, and C) but the simple product was added to a “Product Bundle” (via this Bundle plugin) since it adds an option to edit in the cart:
https://d.pr/i/kxv38F
Clicking that “Edit” link redirects back to the product page, but all of the messaging makes it clear that it is going to update the cart, not add another product to it:
https://d.pr/i/yYXYs6
Is this more in line with what you’re looking for?
