Sounds like you slightly "overcooked" the starch when you ironed it. It should wash out. I wash all my fabric prior to storing, and mostly don't iron it 'til I use it. If I do iron it and I'm storing it, I don't starch it. Apparently, silverfish and related pests absolutely love to eat starch (and the fabric it's on), they really love books too, not just the paper, it's the glue in the bindings that attracts them, the paper, like fabric is an extra so to speak. Hope all is good after a quick wash!