Although the federal funds rate started rising from mid-2004 US long term rates continued to fall. A likely contributory factor to this conundrum was the contemporaneous increase in US bond demand. Using ARDL-based models, which accommodate structural breaks, this paper estimates the impact of demand on US bond yields in the conundrum period. This impact is shown to have been everywhere significantly negative. The fact that our model fully explains the bond yield conundrum gives support to the hypothesis that the US CDO market was rapidly expanded before 2007 chiefly to absorb the overspill of global demand for safe assets