I've been having an absolute mare of a time with the software lately. I think you're right in calling out a software bug. I made a list of my problems:
In itunes I go to sync the phone.
The sync process freezes on ‘step 4 waiting for changes to be applied) and nothing happens from then, so this forces me to cancel the sync (which I can’t do), so I unplug the device.
I then have to exit itunes and re open.
I then sync my phone again, and there is now 50gb of ‘OTHER’ taking up space on my phone.
When looking in settings-storage on the phone it confirms there is only 9gb of storage left on the phone, even though im only actually using 52gb so I should have 60gb left at least.
I ring apple helpline and spend 40 mins on the phone, end up with a factory reset and re-sync.
This gets rid of the 50gb ‘OTHER’
Upon resync I end up with hundreds of ‘greyed out’ songs on the phone (when nothing has actually changed from the previous settings.)
I ring apple, and they say to re-sync.
I re-sync and the 50gb of ‘OTHER’ is added back to the phone, and I can’t sync my music AT ALL
The sync freezes on Step 4 again, I rage.
I'm currently trying my 3rd re-sync, so i'll see how it goes. If I'm still having problems with half my songs being randomly greyed out I might make a genius appointment and even though they might not be able to do anything, at least i'll know that I've tried.
It doesn't make sense that I got all those greyed out tracks, as when I first bought the phone and set it up, everything was perfect. The the latest IOS update hits and boom everything goes pear-shaped.