Got a flat on group ride. One of the members offered his canister to quickly inflate the tire after the repair so that we can get on with the ride. I needed to add a few more psi to the tire so I screwed on the Lezyne and pumped it up a bit more. Unscrewed the pump head and the core came out, as did all of the air. What a waste. I am now on the search for a replacement mini-pump with a locking head...