From a comment I just posted on a bug report on github:
"I've dug up a Windows 7 installation and can confirm the problem is caused by the libimobiledevice stack and iOS8. It most likely needs a newer version in Calibre itself.
I'm currently installing Visual Studio to try and build a new stack myself and test with that. It's entirely possible, though, that the Windows port used (
https://github.com/storoj/libimobiledevice-win32) just doesn't work properly and the "real" libimobiledevice & friends would need to be compiled on Windows but we shall see..."