By adding potential energy to the water column, diapycnal mixing is thought to be one of the driving mechanisms of the meridional overturning circulation (MOC). Today, most state-of-the-art ocean general circulation models calculate the diapycnal background diffusivity independently of the stratification. Results from conceptual models (Nilsson and Walin, 2001), layer models (Marzeion and Drange, 2006), and idealized GCMs (Nilsson and Brostroem, 2003) suggest that a more physical parameterization could lead to fundamental changes of the stability properties of the MOC with respect to freshwater perturbations. Specifically, increased vertical mixing as a result of weakened stratification could lead to an increase of the MOC as a response to freshwater forcing rather than a decrease. We show that while the suggested feedback itself may exist, freshwater forcing will not necessarily result in a weaker stratified ocean, so that it is to be doubted that the feedback will have a major impact on the stability of the MOC.