This afternoon, I ran into a problem with iTunes 8 and iOS 8 on my iPhone 5.  When I connected my iPhone, iTunes said that I had 43 GB of “other” data on my phone.  I had no idea what it was.

After much wrangling, I finally came up with a solution that did work.

On the iPhone, I erased it (Settings -> General -> Reset -> Erase All Content and Settings).  Then, after the iPhone finished erasing, I reconnected it to iTunes, and let it restore from backup.  At first, I thought it didn’t work because the iTunes screen still showed the big yellow bar of “other” data.  A couple of minutes later, it refreshed, and suddenly I had <1GB of “other”.  I did have to reboot my phone and my Mac a couple of times each during this process to get it to work, and I had to sync twice to get all onto the phone.

Whew!

(Edited to add in some reboots.)