I took my son's iPad to the apple store today to get it replaced. It's an iPad 1. I haven't updated to ios5 on this new iPad bc I think it works better on 4 than 5. Anyway, the issue is that each time I download apps I've purchased before, they look like they are downloading and then they disappear. I haven't tried to purchase new apps, but rather, I am just downloading from my already purchased list. What would be making them disappear?