I have three of the Lum mini Dejavoo folders. I haven't had lock-up issues but none of them have good ball detents so they will fling open easily if turned upside down. I don't care for that. I sent Benchmade an email several months ago and never received a response concerning this issue.
I wouldn't let this stop me from buying one. Any Bob Lum design is well worth having. If you go to ebay now you might be able to get the New Spyderco Lum Chinese sprint run in ZDP-189. When those are gone they will be tough to find at a decent price and while you might have to pay $150-$175 for one now they will be $200-$225+ by next year.