The default value of referrer type for an image request is Typed/Bookmarked (ref_type=‘6’). To calculate referrer type correctly, a valid URL must include the standard “http://...” protocol. Otherwise, referrer type is set as Typed/Bookmarked.
Adobe's code includes this protocol by default when generating an image request. Issues generally arise when the referrer is manually set via s.referrer without a protocol.
NOTE: This situation also affects the way Marketing Channels are calculated or the data that shows with breakdowns in Marketing Channels reports.