I notice a little bit of Dexter creeping out in Mac from time to time when he's not trying to be Dexter. Between the facial expressions combined with the tone of voice, Dexter shows himself now and then otherwise.
The first place I noticed it was in "Faith, Hope, and Charity". When Mac and the Lacey sisters are tied up in the cellar and he is asking them if there isn't something more they want to tell him about Leo or the will.
Right now I cannot think of the other place that I particularly noticed it, but it's fun to see Dexter creep into Mac's normal persona. It makes me smile because I think of Dexter then too.