I smoked on second high rack as well.
Could be a few things - too much smoke, or rather too tight a vent. I'm pretty sure that I only put 2 to 2.5 hrs of smoke on, so that should have been fine, but maybe that's too much for residue. I had always felt that if the vent were wide open that all the smoke will just rise along the meat and escape, so I keep a near shut vent. Just enough of a crack to eliminate the backdraft through the side.
However, this past weekend I smoked salmon and some cheese and vented fully to reduce heat. What I found was that when I opened the door, the cabinet was still very full of smoke, and that there should be no fear of lack of smoke with the vent fully opened, so I might try a half open approach in the future. Live and learn.
As a side note, I have owned the Bradley for probably 5 or 6 weeks and smoked every weekend. I have only cleaned the removable stuff - racks, bowl, and of course drip pan. I clean the door seal, but have never yet been "up to my elbows" cleaning out the cabinet. I figured that the more seasoned the cabinet, the better the job of smoking that the unit will do, but perhaps it is time to give it a good clean and re-season the cabinet - maybe that's what's causing my dark outsides[xx(]
Just for fun though, I am going to try a t-shirt or cheesecloth, because that should produce a high quality finish[

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We'll have to swap a batch of chops some day[

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Whitetail[

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John - Lethbridge, AB