Besides the adobe defualt "referrer", we've set up an dimension to record any page refer to the landing page at hit level, internal domain is also included. Try to help us to see any "previous page" before the current one.
It's hard to say what's wrong with your implementation without knowing the details of how you're setting prop33. From your example values, I'd say that it's being set by a script that either returns the referrer's domain name, when the referrer just contains the domain name, otherwise it returns the full referral URL. But that's just my guess.