Yellen starts selling Treasuries to bank billions of profits for US taxpayers on QE and tighten policy.
High beta assets like HY and EM sell off, which causes Treasuries to rally.
Real money which has been forced into high beta assets is left holding the bag. Sovereign and regulated money is left holding a low yield portfolio exposed to duration losses next year.
I guess it should hold until the market focusses on wage inflation and the back end starts to sell off, but that might be a 2018 story.