Bernanke on QE - wrong in practice and theory?

Ben Bernanke  - “The problem with QE is it works in practice, but it doesn’t work in theory.” 

The markets will have another test of QE through the ECB, but what determines success with non-conventional monetary policy? QE in practice and theory seems to have issues. We may find that success is especially hard to measure if we believe the problem has to be reviewed through an entire cycle. We cannot say QE is a success until the QE cycle is finished, and it is becoming hard to decide when the cycle should be reversed.

Six years after the beginning of the recovery we still do not have enough data to say that the QE experiment should start to be reversed. We have stopped adding to the Fed balance sheet, but cash from principal and interest will still be reinvested. It seems as though the earliest the Fed increases rates will be September, so how will this experiment end. Could it be through a slow transition to normalized rates or a volatile path involving market tantrums? My bet is on a transitional tantrum.