referring domain numbers in marketing channel trends very high than normal.

Did other marketing channels (by raw numbers) decline significantly at the same time?

Have you tried to correlate the Marketing Channel (using Marketing Channel Instance to limit the data to when its being set) against the Referring Domain?

Also, while your Marketing Channel rules haven't changed, is it possible someone pushed a tracking update and broke referral tracking.. your "Typed/Bookmarked" also seemed to spike... I wonder if someone broke tracking Referrals in your implementation (as in, as the user navigates from page to page within your site, the previous page isn't being set as a referrer and now every page is treated like an incoming source of traffic when it shouldn't be).