Bah. When I first started experiencing this issue, I couldn't find any threads about it. This must have been shortly before these threads were created because clearly I'm not the only one. I thought I'd just add my voice to the void that Apple will never respond to (but hopefully they'll actually fix it one day right)...
I've tried loads of things to stop this from happening for the last few years, and I had about 6 months maybe where it stopped happening altogether. That was great! However recently those dreaded +1s have started appearing again. At least I know I'm not alone ... Yeah it's not much of a comfort to me either.
I'm really into my music - that's why I use iPhone because to me it's just the fanciest iPod you can buy. However, the fact that I'm so obsessed also means that any procedures that involve re-syncing my music again are rarely something I can afford the time and hassle to do. I have a 70gb music playlist, and a 1.1TB iTunes library. This is on a really powerful computer ... and it still takes between six and EIGHT hours to sync the music completely. (I have the "convert all higher bitrate songs to 128kbps AAC" option enabled, which is probably something to do with this. But iTunes apparently uses a single thread to do the conversion as while it's syncing my very powerful Mac just stays there almost entirely un-utilised. Converting the same amount of songs in an app such as XLD, which uses as many processing threads as you can throw at it (and as much disk I/O), takes under half an hour.)
I like local media for obvious reasons. I also like iPhones. However this means for over a decade now I've had to bear the burden of iTunes for all my iPhone sins. I've watched as the software gained features, became more bloated, FINALLY added "Queue up next" features that made sense (shout out to iTunes DJ/Party Shuffle), and finally recently they took some hardly-even-noticed features out, to the zeroth gain of performance or efficiency. I like the UI now, it's not too bad, but it STUNS me that Apple, literally the world's richest and most admired company, can't make a basic database-driven app work to sync music back and forth. Now, nothing works 100% and is totally bug free. But as we've all seen, iTunes is actually experiencing a regression. If you had, say, a iPod (5th generation) back in 2006, you would have been able to sync your tunes to your heart's desire without this problem.
Apple needs to prioritise this because the people who are hanging on and using iTunes for their local media are likely some of their longest-running, longest-suffering and most dedicated customers. I'm so deeply locked in to the iTunes ecosystem that it will be an epically gargantuan effort to move to another platform, but if I can't get my ridiculously expensive and advanced devices to perform the basic features that I prioritise most, Apple will literally be forcing me to start looking at other solutions.
FIX IT APPLE. (Oh and stop blocking me from purchases I already own because I happen to owe you £5 that you can't think I will get away with not paying you. I'm a poor, ill person. But that's another gripe... More related to how you treat your customers. This thread is about your products NOT WORKING PROPERLY. Is this really so hard to fix? I mean, right now I can bring up my Photos app, type in 'trees' and see all the photos that contain any kind of tree out of my iCloud-hosted photo library which runs at 80gb. BUT YOU CAN'T SYNC MY MUSIC PLAYLISTS WITHOUT CREATING CRUFT THAT I HAVE TO MANUALLY CLEAN OUT EACH TIME? d a m n)