I realize that metadata issues have plagued Xbox Music since it's inception, but I've noticed a new issue that I'm not sure was present on 8 (I tried to stick to the Hub due to the poor performance of the Beta app on 8). When downloading music from cloud collection, metadata is changed, causing the album to be split up. It's not a complete mislabel of metadata, but still causes albums to be split up. Also, I downloaded a song directly from the store, and it removed the artist and album name. I did report it on the Xbox Music update suggestion forum, but figured I'd also post it here, as well.
If you have a Windows 8 PC and have the music downloaded there, you can use the Windows 8 app to share to your phone. Beware though. They've had similar problems in the past with music downloaded to the subscription cache folder on PC, even though the music in the app appeared normal (part of the reason I decided to download instead of transferring in the first place,) so you may just want to double check the actual files and re-download any albums that need corrected. It's an arduous process, yes (I personally plan on dedicating a couple hours tomorrow to fix things on my end,) but where it appears to be corrected on Windows 8 end of things, it absolutely does not work right on Windows Phone 8.1. For now, it's the only way to have cloud music available offline without your collection looking fractured.
From my own experience, it's mainly an issue with albums that have extra info like (Parental Advisory) or (Deluxe) in the album name. Just so you have an idea of what to look for.