Quote from earlier in the thread:
'It is the fact that (R,R) and (S,R) are in racemic (1:1) ratio that the R configuration rotation at C-1 will cancel the S configuration rotation at C-1.'
A 50:50 mixture of (R,R) and (S,R) is not a racemaic mixture, since RR is not the enantiomer of SR. These are mixtures of diasteromers. Even if you assume equal amounts of each diastereomers, there is no reason to believe their optical rotations would cancel.