I would recommend trying again but this time wipe both the cache and dalvik cache, this won't touch your data so you don't have to worry about it.
Not knowing an extremely large amount about android I can't say the following with certainty but it holds true in some other situations: system cache in some OS environments can be placed on a separate partition than the primary system, honestly I would assume that's how it is done on the phones.
If that is the case than you would get a false reading when looking at the memory left cause it wouldn't account for the cache in the first place... Again that may not be the case at all, I'm really not certain. Just don't know enough about android at this time. But I would still recommend wiping both cache and try again.
Last thing, good luck; and let us know how it turns out.