iPhone 5 (6.1.4)
OS X (10.8.4)
I haven't had any issues synching until I noticed a couple items that I created on iPhone weren't appearing in Calendar on my MBP. I'm not using iCloud to sync. I'm synching with iTunes via USB.
I have created items in the Calendar on MBP and they synch to the iPhone without issue. I can modify those items on the MBP and those changes are reflected on the iPhone after synching.
I have use TimeMachine to backup MBP and back up iPhone with iTunes at each synch.