I'm playing the Hexxit modpack and have made a couple of Tinker's Construct Cleavers, which are supposed to have a Beheading trait by default, but they have thus far given me no increased rate of mob head drops. I then explicitly added the Beheading trait to one of them and ran around killing many things, but still my trophy wall of heads remains without any new tenants.
I'm quite disappointed at my lack of decapitation capabilities. Is this a known bug, a configuration issue, or some third thing?