Yep, I had the same when tracks were missing from a Chase & Status album I purchased in Feb this year. Here is what I sent to Apple for investigation:
I was sorting through my iTunes albums using my MacBook Pro yesterday, and noticed that an album I had purchased in February had tracks missing.
I went to the Purchases tab and the album was not showing in my purchases, so I went to the iTunes Store, but the album was (and still is) showing as 'purchased' and the button is greyed out (you can normally re-download purchases this way but not this time!).
I also turned Match off and went to my account via the Store tab to check for available hidden downloads in the Cloud, but it said there were no available downloads.
I thought I may as well delete the tracks of the album that were still showing in my library, in case the greyed out 'purchased' in the store will then let me re-download the album once all traces were removed, but sadly there was no change.
I then decided that as the full album was still on my iPhone, I will transfer the album back to my iTunes library by using the transferring purchases option.
This worked, but there are several anomalies, which are:
1. The album is still not showing in my purchases
2. If I accidentally delete the album, I cannot see how I will get the album back, especially if I decided not to renew my Match subscription!
3. When I right click any track from this particular album, and go to the Summary tab, it states that I purchased the album yesterday (29 Aug 2013), when I purchased it back in February, as per the order number I have provided!
If anyone here at MR Forums knows any fixes, then it will be much appreciated - ever since iTunes 11 was released, it just seems to be glitch after glitch 🙁