  In the context of the Supersymmetric Standard Model with hierarchical
sfermion masses, we re-analyze the QCD corrections to Delta F=2 effective
Hamiltonian properly including effects which have been neglected so far. The
point is that some Delta F=2 diagrams, involving both the heavy and the light
sparticles, exhibit a logarithmic dependence on the ratio between the two
masses, signalling a sensitivity to all the momenta between the two scales. In
order to properly deal with these terms one has to take into account the mixing
between Delta F=1 and Delta F=2 operators. In typical situations this treatment
can affect the result at the level of 30% or even more.
