I would recommend that you clip the knife to the edge of the pocket so that the back of the blade has something to rest against. I would never carry a tip up folder clipped to the middle of a pocket where it can come open.
I now own Kelly's "Senator" sebenza, and I did notice that it does come open when I pull it out of my pocket more often than my other sebenza. My other sebenza has only opened when I drew it one time in the 2 years I have been carrying it. It opened because a loose thread actually worked its way around the thumb stud, and so, it would not matter what kind of lock system you had keeping the knife closed, it would still have opened. I am not sure why Kelly's sebenza opens more often when I draw it; both sebenza's have similar ball detent pressure keeping the blades closed. The only thing I can think of is, the handle on Kelly's sebenza is noticably thinner than my older sebenza. Mine was made in '97, whereas Kelly's was made in '98. I don't know why it is thinner, or how thick current sebenzas are, but because of the thinner handle slab, the thumb stud protrudes more. I'd also like to mention that Kelly did send his sebenza back to the factory and Chris rounded the thumb stud so the ridges wouldn't be so catchy, and I believe, deepened the detent hole. It still opens when drawn though. It is still rare that this happens though.