Re-downloading not the answer. Songs are stuck in Purchases.

Question

I've subscribed to and used iTunes Match since it was first offered. I have also had a consistent problem with it from that day. On my main computer, any song purchases, songs added to the Library, or songs imported from CDs appear in the Purchased source list. And there they stay. No amount of time makes them appear in the Music source. The songs are physically in the Library, they're in their proper folders; they will just not move into the Music source. I can't drag them from Purchases to Music. I can't drag them to connected devices. I can play them. I can edit thier tags, if necessary. They're just stuck. This also happens with iTunes-compatible formats of home-movies and videos, though I don't know where the heck they go -- they just don't appear in the Movies source when imported into iTunes.
Quitting iTunes Match solves the problem immediately. Songs instantaneously move into Music, and Movies appear in Movies. Once they've moved, re-adding the computer to iTunes Match causes those same items to be synchronized to all the other devices that are linked to that account.
I should note that purchases made on satellite devices get downloaded and added to the Music source almost immediately on launching iTunes on the main box.
Does this sound familiar to anyone, and are there any helpful tips available for investigating this. I have disabled or uninstalled any "social" hooks into iTunes, like Scrobbling from Last.FM, etc.
Thanks.

Answer 1

Apple's official advice on duplicates is here: Find and remove duplicate items in your iTunes library. It is a manual process and the article fails to explain some of the potential pitfalls such as lost ratings and playlist membership, or that sometimes the same file can be represented by multiple entries in the library and that deleting one and recycling the file will break the other.
Use Shift > View > Show Exact Duplicate Items to display duplicates as this is normally a more useful selection. You need to manually select all but one of each group to remove. Sorting the list by Date Added may make it easier to select the appropriate tracks, however this works best when performed immediately after the dupes have been created.  If you have multiple entries in iTunes connected to the same file on the hard drive then don't send to the recycle bin.
Use my DeDuper script if you're not sure, don't want to do it by hand, or want to preserve ratings, play counts and playlist membership. See this thread for background, this post for detailed instructions, and please take note of the warning to backup your library before deduping.
(If you don't see the menu bar press ALT to show it temporarily or CTRL+B to keep it displayed.)
The most recent version of the script can tidy dead links as long as there is at least one live duplicate to merge stats and playlist membership to and should cope sensibly when the same file has been added via multiple paths.
See also Make a split library portable for some thoughts on best practice when it comes to organizing the library and media files.
tt2