OOG: 2-handed Str 16 Power Attack 4 should be 1d8+12 (1.5xStr is 4, +2xPA penalty is 8); I don't know where 1d8+7 comes from. Since the lost two rolls were in fact misses, which gives rather a wide swing in outcomes, I re-rolled... and wouldn't you know, again rolled a hit with maximum damage...