I had that with mine. There was a considerable amount of rusting around the bell housing and also the disc itself was rusty and not fully utilised. It's taken about 5k miles to sort the disc rust out and a whole day of wire brushing, scrubbing and re-painting (bell and caliper) to do the rest.
I always use a long brush to clean the inside of the alloy every weekend too. Keeps them looking as good as new. It's no use having a clean outer and dirty inner with these wheels. Just looks wrong IMO.