First, he's Just flicking it back and fourth. It's not Showing if it's a tight lock-up. Like a Broken OTF or Gravity knife that doesn't lock anymore. Just that the blade's still moving. I got some pants/jeans fuzz on/in/caught the spring that pulls the pin forward on my 710 and it wouldn't fully engage. one side was pulling and the other was not, so I could still flick it open and closed, but if I stabbed something it would have defiantly folded on me. If BOTH sides of the pin aren't in the tang, or the spring is caught with something(ie:dirt, fuzzy wuzzies) the little springs that pull the pin can give you problem.
Take it apart and see how it works. Oh, Don't. That's a Void on the warranty:-(