I think he is saying that BS2 is calculating an incorrect (too high) post-boil gravity based on his boil-off rate.
Calculated pre-boil = 1.033 @ 7 gallons (231 points)
Calculated post-boil = 1.041 @ 6 gallons (246 points)...where did the 15 extra points come from?
His actual pre-boil is the same as BS, but actual post-boil is 1.039 @ 6 gallons = 234 points.
I haven't had a chance to play with this, and see if there is a way to force BS2 to create gravity points during the boil. I'm pretty sure I don't have this issue, but I wouldn't sweat 2 points of SG (that's within my tolerance of good enough). So, I can't be sure I would take note of a consistent 0.002 low reading. I WOULD notice 4 points in 70, though. If it is a linear error...I would certainly catch that. 1 Plato is where I draw the line, and look for a cause.
I did NOT have this issue with my pliny batch (I was dead on at 1.070 OG) on Sunday.