"A common misconception is that the DV01 of a Treasury security remains fixed as the yield of the instrument changes. In truth, the price-yield relationship of a Treasury security is nonlinear; as yields fluctuate, the DV01 of a Treasury security changes" http://www.cmegroup.com/trading/int...g_U.S.Treasury_Futures_Conversion_Factors.pdf
BTW, look at the statistical correlation - it's complete shit, the Daily closing correlation is like in the low 64% last time I looked. And you won't get a SPAN margin credit on it either.