I'm Appletarded, and get confused by a lot of Apple software. I don't know how I did it, but it's happened on three separate occasions. Twice on a Windows PC and once on a Mac. Somehow my misunderstanding of the sync feature led to the PC getting what was on the iPod, and the music collection on the PC being deleted. It was many years ago; I eventually learned my lesson and stopped trying to use the damned thing. Maybe it's better/safer now. But, I'll never find out, as I can't think of any reason I'd have to use iTunes.
Seems like that would be the way things would work, wouldn't it? Again, it's been many years since it happened. The precise details of what happened are a bit fuzzy at this point, as is often the case with very painful events in life. It may have merely "forgotten" where to find all the music and emptied the library. And, it may be that the actual file deletions happened on the iPod rather than the PC (I'm still pretty sure it deleted files on the PC, though). I remember being furious and confused by the behavior of the software...and I remember having to re-rip several albums that I hadn't backed up lately, and I lost a few mixtapes that someone had made for me.
That reminds me of another thing I hated about iTunes...it was always re-indexing its library. All the damned time. Every time I would start it, it would go galloping all over my PC (this was back in the days when I had three or four hard disks, plus a file server) for like 30 minutes.
Regardless of the specifics, iTunes made an enemy for life out of me by being so damned confusing, and so hostile to my existing workflow. I'd been using digital music for a decade before iTunes came along, and iTunes just did not fit into how I'd been using it.
I've done this before, but on Windows. There was a setting with an older version of iTunes on Windows where it would automatically manage your music, which means that it moves it around and takes ownership of it. If you try to delete something from your itunes library, that you thought you copied, it would actually delete your music, not the link between itunes and your music.
Has happened to me on several occasions, especially with an older iPod shuffle. Synced in some music, then set everything I could find to "manually manage music" and "do not autosync". Moved the source files around on the PC, and the next time I connected the iPod, iTunes "helpfully" automatically wiped all the music off the iPod, since it could no longer find it in its library.
I've heard others getting burned in a similar fashion. One person needed to charge the iPod before a long flight, and didn't bother connecting the external drives containing all the music. Only after getting on the plane did he realize iTunes has "synced" his "empty library" and blown away everything on the iPod.
Back in the early days of iTunes, I bought an iPod Mini and synced it on a Windows machine. Occasionally, I would sync my iPod, and something like 20 songs would disappear (purchased and non-purchased). This happened without warning, with alarming frequency.
This was a known bug as late as iTunes 7, which would sometimes disregard the "Automatic Media Folder Management" setting, do it anyways, and sometimes files/folders.
Happened to me as well. Many years ago I used Itunes and it wiped my collection off, since I was using automatic syncing. I guess this fixed it now, but I have moved away from iTunes since then.
I currently have two copies (pointing to the same file) of most of my music collection in iTunes. No idea how to fix it. It happened when I tried to import some MP3s from an old laptop that had some overlap.
* Change library location back to original location.
* Wait 30+ minutes while iTunes freezes rescanning you library (I haven't used iTunes on Mac but on Windows it is a horrible experince, seriously haven't they heard of threads?).
What? Ummmm....even my super non-techie wife hasn't done that.