Let me get this straight: you pulled out 2 different bindings out 2 different skis, 2 seasons in a row?
So either way you've just had bad luck 2 times in a row or your shop has messed up (since i understand both skis were mounted at the same shop? right?)
now i don't wanna go point finger at your shop but things seem like it...
All the reasons i can think of (right now) why bindings would rip out are:
Shop-related:
_Didn't use the jig correctly (or didn't use one at all) and drilled the holes slightly wrong, thereby causing unnecessary tension between the screwholes...
_Drilled the holes too big for the screws (used the wrong drill...)
_Didn't seal off the drillhole with some sort of woodglue to keep water out (reason; water slowly penetrates your core through the drillholes; softens up the wood and your binding rips out)
_Overtightened the screw; recommended force = 4-5 newton-meter force/screw.(this strips the drillhole and makes it too big for the screw; same result as drilling too big...)
_The shop used the wrong screws; they were too short for your binding/ski
Not shop related:
_You did some realy gnarly stuff on your skis.
_You stored them somewhere cold and moist
_ you didn't fix core shots and water penetrated to your wood core
_The binding is crooked; when the binding is let's say "bent" in some way (highly unlikely) it can topple and rip out bindings (it has extreme leverage)
_Your screws loosened up (can also be shops fault, but this can happen...) your binding vibrates the screws out off the ski...
_manufacturing error; skimanufacturing mishaps happen more often than you'd think....
_backward brake: I've seen bindings get ripped out by binding brakes: when you ski very fast and your ski ejects and lands somehow backwards in the snow, your brake digs into the snowpack and the forward momentum of your ski causes the brakeplate that's attached to the binding to come off... (very unlikely but i've seen it happen; might also 've been due to other unknown issues with the ski/binding)
so now you know as much as i do; draw your conclusions....