I've had this happen to me a few times over the years. Once I just let the gas slowly fizz out of the leaky valve since we were heading back to the car anyway. The other time I screwed it back onto the stove to stop the leaking. I can't say for sure whether they malfunctioned (the valves are very simple) or some piece of foreign material got wedged in there but I'd guess it was the latter.
Nuts -- why is that mixture not the best for you, is it because you are going to use it in cold weather? Winter snow camping is the only time I steer clear of the n-butane based canisters like that one. The rest of the time I buy the cheapest gas canisters available. I would buy those if it saved me $0.10 per canister but they don't sell them close to home.
If you still have one of the canisters and you're curious try poking it to depress the spring and see what happens. Then cut it open and inspect the valve from below.
Statistics: Posted by Orion — Wed 30 Apr, 2014 1:04 am