iTunes keeps downloading duplicate items
I'm not sure if I'm submitting this to the right forum, as I'm not sure if it's an application issue or a store issue. I downloaded a TV series from the store, my first TV show purchase after iTunes 11 was released. On several occasions now, it has downloaded duplicates of episodes, the first being the day I purchased it! It downloads a duplicate which then it says has not been watched, adds a file to the library with a sequencial number, and proudly shows the duplicate in the library. The only way I've found to solve it is to delete the affected files, and re-download them again, as if I simply delete the duplicates it shows up as being available on iCloud! Does anyone know why it would be doing this?
If it helps, I'm running a late 2009 Mac Mini, with the latest version of OSX and iTunes, and my library is stored on an external drive which is never removed.
Mac mini, Mac OS X (10.6.7)