There appears to be a bug with iOS 5.x when re-downloading multiple apps. I have observed this on iOS 5.0 on an iPhone 3GS, and 5.1 on an iPhone4S, an iPad2 and a 2012 iPad (the “new” iPad).
When you click the iCloud “re-download” button you aren’t taken out of the AppStore and back to the home screen like if you had clicked “Install” from the app page. The app simply starts downloading and you remain the in AppStore app. If you return to the home screen at this point then you will see the app downloading and everything is fine. However if you re-download multiple apps in this fashion without returning to the home screen then things will be strange when you do click the home button.
What appears to happen is that only the very last app you selected to re-download appears with the “waiting” text. The other apps that are “waiting”, “downloading” or “installing” do not appear. They do not appear until they finish downloading and install, at which point their icons suddenly pop into existence. I think this is a bug.
If one of the “hidden” apps is very large (like a game for instance) then it can seem like the download is stuck on the app that is visible with “waiting”. It isn’t. You just have to wait for the ones that you can’t see. Because you can’t see them you can’t stop them downloading. You can stop the ones that are too big to download over 3G/4G/LTE by switching off WIFI.
I suspect that this could be the cause of at least some of the apps stuck at “waiting” complaints I stumbled across while trying to figure this out.