the shop is probably drilling with a 4.1mm which is larger than the standard 3.6mm bit because they have the titanium in them, so what happens is all the pressure is placed on the titanium layer and there's not much bite into the core of the ski.
What I would suggest you do is mount the new pair with a 3.6mm bit then counter sink the holes ever so slightly. When I say slight, I mean, just enough to take the sharp edge off the hole. Mount up with some epoxy in the screw holes and it shouldn't give you any issues.