This works as designed for QuickBooks, jkabbe.

Changing the product/service items on an existing invoice will remove or change the description, rate, quantity, and others. Thus, keeping the invoice up to date.

You can take note of the invoice details by taking a screenshot. You can use the Snipping Tool on your computer accessories, too. Then use the screenshot as a reference when updating the invoice and reenter the details.

Let me know if you have other concerns. I'll be around.