Surprise! CarMax's profits were supposed to go up, but they crashed down instead.CarMax (KMX -19.40%) turned into a one-car pileup Thursday, falling 19.7% through 2:15 p.m. ET after reporting worse-than-expected earnings for its fiscal second quarter, ended Aug. 31.Heading into the report, analysts forecast a strong quarter for the used car dealer, with earnings of $1.03 per share on$7 billion in sales. Instead, CarMax's profit was only $0.64 per share, and sales were only$6.6 billion. CarMax Q2 earnings ...