Keeps dropping the final picture

When using a generated image as the starting point for a new prompt, the product completely disappears and returns a blank or empty image. This has happened multiple times in the same session on the same product. The sign was successfully generated in a previous step but when I try to add a background using that image as input, Nano drops the entire product and returns nothing. This is a repeated failure on background-change prompts when using AI-generated images as the source. The prompt was simple: "Hang this sign on a classroom door. Blurred hallway background behind it." The product should have stayed exactly the same with only the background changed.