I think there is some sort of link as to why some people do better without revision in subjective subjects like English, history, politics etc. Because when you first sit the paper after doing lots of revision, you're determined to get the highest grade you can personally get. You're tensed, worried and scared if you don't get it. after you've received an E for that exam you revised like hell for, you lose faith in doing well on the subject and stop revising.you sit the resit thinking you're gonna do s*** because you haven't revised but in fact, you're relaxed because you think you're not putting any effort in cos you're going to fail, as you haven't revised. Things that you had revised for the previous paper comes back to you, but you're answering the questions in a calm, relaxed manner.
This is the only reason I can think of for not revising and getting a higher grade in your resit, though I'm not saying the exam boards are 100% perfect and reliable.
Stress/tension can do wonders you know.