Imagine hosting a cocktail party with guests arriving and departing at random times.  A particularly rowdy and unpleasant guest--let's call them "August"--was finally talked into leaving.  Moments later the doorbell rings.  The new guest looks just like August, but with an obviously fake mustache and perhaps a wig.  The guest claims to be "September," but their behavior seems all too familiar. 

All that to say that the first few hours of trading in September have done nothing to push back against the pervasive selling trend in August.  Indeed, sometimes a shift in momentum is as simple as the change from one month to the next, but in the current case, bonds remain data dependent.  Stocks too, for that matter.  The quintessential "Fed accommodation trade" involves anything that promotes tighter Fed policy resulting in weakness for both stocks and bonds.  It's typically seen at times when the Fed policy outlook is subject to change and debate (like now).