I noticed it a while back, but was finally able to reproduce it...

Sometimes I got the confirmation pop-up asking me to purchase an item, while I didn't select any item. This usually happened when I tried to exit CS. It also appears this happens on iPad only. If you touch the area marked in the picture below, you'll get that confirmation popup. So it's basically asking your permission to buy... 'nothing'.

It's not a big deal really, because you don't loose any gold if you choose 'purchase item'. I just wanted to point it out. It's kind of strange, when mis-tapping the exit button, you'll get that screen.