It is the album, it's just more complicated
(A short lesson is needed):
iTunes is a very large, very powerful tool.
It primarily manages files for your iPod.
Here is the basic play out of its file categorization process:
Album
Artist
Song Title
We're going to focus on Albums. The iTunes Store is the largest collection of products in one place in human history (More than 11 million different files). Most of the the files are songs, they come from approximately half of a million albums. Some of the albums are the relative same.
Meaning, different versions of the same album (i.e. Album (and another version) Album [Deluxe Edition]).
When the iTunes Music Manager processes album artwork or what artist or song you downloaded, it uses information from the iTunes Store, you can also think of it as a database. If the information isn't in the database, it can't process the information correctly (but that's a problem for someone else to face, not you, not now).
On to your problem.
As you may have figured out by this point, the problem is the album has at least two versions in the iTunes database. You might have bought a deluxe version, or an extended edition of the album and some of the songs might not have been on the original album.
As for the solution, it's extremely difficult to fix, but if you really want me to, I'll tell you how.
But I offer an alternative.
Create a new playlist, name it the title of the album (or whatever you wish) and copy all of the songs from the album into it.
Presto, your "album" is ready to go!