Blood Ties.

((I've realized that some people might be confused by 'targeted Occlumens', as I've chosen to call it, for want of a better term. Basically, it is a process involving magical hypnosis in which Harry carefully blocks off the more dangerous parts of his personality and his life, dangerous in reguards to Voldemort, at least. It's somewhat like actively constructing a second personality, one that lacks his more admirable qualities and enhances his least attractive ones. Snape reasoned that Harry would come under attack from Voldemort, through their connection and through more mundane means, and that this targeted attack would be far stronger than he'd used on others. Voldemort -fears- Harry, so he would naturally put every effort behind determining if Harry's act was real or not. The only fool-proof manner of preventing Voldemort from discovering the truth was to make the lie reality. Thus, the version of Harry that exists around Voldemort is -truly- evil, and until Draco speaks his own name, that is the 'real' Harry. Obviously they couldn't do this at any other time, because otherwise Harry would be a danger to other students, especially his old friends. I hope that clears up any possible questions you might have had.

Oh, and thank you all for reading and reviewing. Next chapter to follow shortly.))