The 0640 runs on PB washers as well. It’s a nice knife and I can see why it’s got a solid fan base.
My 0850 can be shaken out, but it needs to be done purposefully. The detent is strong enough that it flicks open nicely and I’m not concerned about unwanted pocket openings, etc. I just assumed it was a consequence of a relatively heavy blade. If you do send yours in, I'd be interested in knowing what comes of it.