Why is my iPad 2 always re-downloading the same app from the app store?

This is driving me utterly insane and it's been going on for months.

I downloaded a game called Companions from the App Store (on the iPad, not on my Mac) ages and ages ago. At the time, the download failed for some reason (got a "please try again later" message), so I redownloaded and everything seemed fine. Until I went and bought another app, the same way, and for some reason my iPad started downloading Companions again. This really annoyed me, so I deleted it, and again everything was fine. Until I went to buy another app.

Now, when I buy an app, I get this really annoying message pop up (usually as I'm halfway through typing my password) which says "Companions and 10 other apps could not be downloaded. Please try again later". The icon for Companions appears on my iPad again with an empty progress bar across it, which starts to fill up once the device has finished downloading the app.

It appears there's some kind of download queue problem, but I've been looking for days for a download queue attached to my itunes account, either in itunes, on my ipad, via the iCloud website, or on my Mac, but no such thing seems to exist. So where on earth is my iPad getting this instruction to download Companions from?

I've got auto-download switched off for everything, including apps, before anyone suggests that. Can somebody please help me before the last fragile vestiges of my sanity slip away? If I see that message one more time, I'll go completely crazy.