When I update my vanilla server from 1.7.10 to 1.8 all types of 2-block high bushes and flowers do gets somehow affected. Most of them gets destroyed immediately when the chunk finish loading and you can pick up their items left behind.
Some are first cut in half were you only se the bottom part of the bush, later these bushes gets automatically destroyed too and you can pick it up. The ferns bushes disappears without a trace.
However, some bushes placed in the server do survive the update. Its very random. Even in the same garden arrangement it can be 50/50 of what will be affected or not of the same kind of bush or flower.
No small flower affected by this bug.