The lie in ANH could just be Obi-Wan covering up the fact that he killed Anakin, which would alarm Luke quite a bit.
Yeah, but if Obi kills Anakin not knowing he is Vader that would be a little strange in ROTJ when Yoda and Obi seam to know it. I guess we could assume that they discovered the truth between EP3 and EP4; or add a scene in our "new prequels" where Yoda tells Obi that the Jedi have discovered the identity of Vader but the audience never knows until ESB.
God it's tricky.