All of my guitars have the double locking system except my EBMM and that's the only one that ever goes out of tune. One tip is to tune everthing up ever so slightly lower than key. Eg, the E should be tuned to about 1/8th of a tone from true E. The reason being, when you tighten the nut at the headstock it will put some additional tension on the strings and raise the pitch slightly. From here you can fine tune from the bridge. Just be sure to properly stretch the strings before you try locking up, I usually give them serious abuse for about 2 days before tightening up.