Alert time discrepancies when synchronizing calendars between iOS 6 and OS X 10.8
Assuming you can still reproduce this on the current version of iOS and OS X, this would be a great bug report to get engineering to fix whatever is causing the data to not sync.

You only need a free developer account to submit the bug report:


https://developer.apple.com/bugreporter/


It looks from your description that you're not making any configuration mistakes, but I'd re-do both account setup steps before filing a bug to be sure your case is reproducible.