ORIGINAL: Jezmo
In most ignitions the shield IS grounded through the plug. Think DA50 and all the clones out there. It seems, in your case, the braid is not making good contact with the metal cap that goes over the plug so you will have to ground it as you have and just make it permanent.
Just for curiosity what make of engine/ignition is it?
Sounds to me like the metal cap isn't pushed all the way on the plug! These push on hard the first time or two and many newbies fail to push it on far enough. When in place, the hex part of the sparkplug will be covered.