Event exceptions

These are the sticking point for interop. Major players don't handle EXDATE/EXRULE (either at all or just in the same way), and those really are insufficient for just changing a single instance of a recurring meeting. So ownCloud likely is just trying to work with the lowest common denominator.

This problem also kills migrating between calendar systems. Everyone gets to claim "interoperability by standards conformance" without ever interoperating in a way that might lose customers. I know I have to reschedule individual meetings frequently but cannot lose the general recurring pattern...