I've got one that is called a 7DEX but it's just a #7 with a plastic shroud on it. (http://www.masterlockimages.com/CategoryResults.cfm?div=29&cat=504&cat_parent=437&series=440)
It's been giving me similar problems. I've gotten it a couple times but admitedly it was just by dumb luck. I've started going pin-by-pin and seem to have better luck but I still can't get it "on demand". I like to use a slim-line reach-ball pick on it, it's just about perfect for this lock: (http://www.lockpicks.com/index.asp?PageAction=VIEWPROD&ProdID=382)