So I downloaded Lion for my macbook pro earlier from the app store and installed it all fine and encountered no problems. Then I planned on downloading it for my iMac via the app store again. As I'd hoped on my iMac's app store the lion page simply had an 'Install' button when I was signed in with my appled ID. Unfortunately I decided against downloading it there and then since I was busy later in the day and decided to do it at a later time. Came back to it this evening and now that button on my iMac's app store now says £20.99 and when clicked on then comes up with, 'Buy app'. If I go ahead with this will it charge me? And why has it changed from the simple 'install' that I had earlier? I've doubled checked and I am defiantly signed in on my iMac's app store with my apple ID so I'm doubly confused. Any help?