OpenStack nova resize "ERROR: Resize requires a change in size"

If you get this error when you try to resize an OpenStack instance:

# nova resize example 23 --poll
ERROR: Resize requires a change in size. (HTTP 400)

You need to change your flavor to have a different memory size. It's a bug in an older OpenStack version:

        # /nova/compute/api.py
        if (current_memory_mb == new_memory_mb) and flavor_id:		
            raise exception.CannotResizeToSameSize()