iTunes is a bug-fest
It is my opinion that iTunes, which is supposed to be an Apple premier product, is the most buggy product they offer. I continually have to find work-arounds for it's bad behavior, it constantly needs a force quit and restart, stuff like that. The upgrade to iOS8 on my iPad Air was problematic, but finally completed (iTunes kept wanting to offer me the iOS 8 upgrade while I was in the middle of the upgrade!)
So having to shut down the devices (iPhone, iPod Touch, and iPad) is no surprise to get them to go back to wi-fi syncing. It is what I have come to expect from this buggy iTunes software!
All that said, I still love these devices and cannot wait for my iPhone 6 Plus!🙂