When i'm browsing the ITMS, i get prompted constantly to sign in to purchase music. It happens when i double click to listen to a preview about half the time. Does anyone else know why this is? i first noticed it when they came out with the new store, when it came out for windoze. my worry is that if i stay signed in, it will make a purchase instead of previewing the song. also, is there a way to cancel a download and purchase once it begins?