Yep, I agree with this.
I did A-level Maths (OCR MEI board), and I don't know what it was about the exam board but it just didn't seem to like me. I was fine in class, finishing work way before anyone else and getting it all correct. However:
C1: first time - D, second time - B
C2: first time - U, second time - E, third time - B
C3: first time - E, second time - C
C4: first time - U (couldn't retake as did it in the June of second year)
M1: first time - U (didn't retake)
S1: first time - D (couldn't retake as did in June of A2 year)
The S1 result was the one that I was most annoyed about. On practice papers (which I did a lot of) I always came out with B's and A's and occasionally an A*, so I have no idea what happened in the exam.
Ended up with BBBD at A-level (B's in Law, Government & Politics and General Studies, and the D in Maths)
Got an A for Maths GCSE as well - funny how the 2 subjects I took at GCSE (Maths, and Drama) were the ones I did worst in (got an E for Drama at AS, the teachers blatantly hated me as I wasn't a typical "drama kid", have Aspergers and dyspraxia - they always tried to get me to do things that they knew I'd find difficult, and never helped me with anything like how they did the other students, the final straw was when they forced me to play a disabled girl for a monologue performance).
Nice end to the story though - I'm at a uni I love, doing a course I love, so that Maths A-level doesn't really matter.