Everything I change in iTunes reverts.

Question

Something is very, very wrong.
Song names, album names, album art, playlist names, playlist content, etc., etc, etc... When I change them, they revert.
This has been going on for over a week, now. Since Wednesday, I've changed the metadata on certain albums or songs as many as 10 or 12 times. Generally speaking, all changes revert -- sometimes within a few minutes, sometimes an hour or more later.
I'm not a novice. I'm actually the one my friends call to help them fix their Mac and iPhone problems. I have 3 Macs (all running Mountain Lion), an iPhone, and an iPad. This all began when music I'd added to iTunes on my MacBook Pro wasn't showing up on my iPhone. Eventually I turned off iTunes Match on the iPhone, logged out of my account, then logged back in to see if it would populate correctly. It did not.
So I disabled Match on both the iPhone and iPad, and turned to concentrate on the computers.
The new music I added to iTunes is fine, but then I noticed that several albums whose info I'd modified a week ago had reverted to their original state. So, I fixed that, but noticed a few others. So, while watching TV, I started browsing through album view, fixing whatever needed to be fixed. But then, I'd see -- an hour or so later -- that all of those changes had reverted to their original state. For the last few days, I've spent hours changing metadata (while watching TV -- lol), only to have it all revert.
After reading thread after thread, I followed the advice I saw a few times:
Turn off iTunes Match while holding down the Option key, then sign out of my account, then quit iTunes while holding down the Option key, then restart the computer, then fire everything back up. I disabled everything on all 3 Macs, and I'm now working in iTunes on just one of them -- desperately just trying to get the info on that one machine correct, thinking that I can then populate that data over to the other computers and devices.
Except I can't get the data to "stay still," even on this one Mac! This is beyond frustrating.
In one particular case, I have 17 albums by one artist -- most of which came from the CDs in a box set. But I prefer to show albums with their original artwork, so I had split them into the 17 albums. However, I had used an odd naming convention in the Album field, something like this:
BoxSet - 1|OriginalTitle1
BoxSet - 2|OriginalTitle2
...and so forth, for all 17 albums. Well, I decided that was cumbersome, so I changed them all to just their original titles, and renumbered everything with Doug's "Albumize" script. Everything was perfect. But 20 minutes later -- they were all back with the long names I had assigned, some time ago.
I've tried all sorts of things I've read in threads, including selecting "Update iTunes Match" immediately following the modification of data. I'm fully aware that we shouldn't have to do that -- it's supposed to be automatic. But I'm desperate. I also realized that most of those had been ripped at 192k, so (upon the advice someone in of another thread), I deleted those files (but not from iTunes Match), then redownloaded them at 256k, then again selected "Update iTunes Match."
I've just been throwing "the kitchen sink" at this problem.
Last night, I'd say about 40-50% of those 17 albums seeme "stable." Today I've replaced the others another several times, and now about 15 of the albums seem stable. But it seems like I could wake up tomorrow and find that a few of them have reverted again.
The same is occurring on individual songs that I've modified -- metadata, artwork, whatever.
I'm losing my mind, here -- and this is just with one computer signed into iTunes Match. I'm afraid of what might happen when I begin connecting my other computers and devices back to the service.
It's as if Match isn't keeping track of which changes are new. It's defaulting to old data, instead of giving priority to new data.
If anyone has any further suggestions, they'd be most welcome. With no one from Apple officially monitoring or replying to these discussions, one wonders if they're even aware of these issues.

Answer 1

Well, that's just it -- the deletions weren't replicating, so they were in fact a major issue.  :-)  Although the metadata within individual songs stabilized, the playlists still had a mind of their own: If I deleted one, it would reappear in less than 5 minutes; if I renamed or modified one, it would revert to its previous state.
So, I ended up doing the "worst-case-scenario" reset.
I encountered a few inconsistencies between that article and what I experienced, as well as some easier ways to do things.
For example, he has a protracted way of forcing iTunes to create a new, temporary library, when all it takes is either renaming the iTunes library or just moving it to the desktop.) I also had to force iTunes to create a new library a total of 3 times, as it seemed to get "stuck" after I'd deleted several thousand tracks and would refuse to allow me to delete any more. Anyway, those steps, in combination with sometimes waiting overnight for things to settle, got me 99% of the way back. (I'm sharing these details for the benefit of other readers.)
Even after completing that process, I still had some stubborn playlists. But after waiting overnight (again), I was finally able to delete those.
BTW, I highly recommend Playlist Manager (donationware; I'm not affiliated), which dramatically sped up the process for me:
http://dougscripts.com/itunes/scripts/ss.php?sp=playlistmanager
It allowe me to save (export) all of my playlists to a folder in one step.
Finally, after getting my MacBook Pro back to normal, I chose to turn iTunes Match back on -- first on my iPhone. After a few hours, all seemed OK, but a few, stubborn playlists on my MBP simply would not show up on my iPhone, even after jiggering them by changing a name or adding a song. In those cases, I deleted the current copy of the playlist, then reimported it using Playlist Manager -- then, magically, they appeared on the iPhone within a few minutes.
For now, I'm omitting the notes I took while performing the "worst-case-scenario" reset. But if anyone thinks those notes would be helpful, I can post them later.
And thanks again, mracole, for your input!