Just stumbled across this, I had two of these "Spundy" valves earlier this year as well. They kept popping off on my corny kegs posts. I got them from Brewdaysupplies and they were very good about it and refunded me. They said I wasn't the first person to have issues and said they were going to stop stocking them as a result.
Shame, the price and form factor was good but they were effectively useless, wouldn't recommend them at all.