IC - is this what you're referring to for butane canisters -   (You need to Login or Register And can you be more specific about what MRS stove you have?  I have experience with several models, but never had the situation you describe occur.  My first thought is did you possibly leave the valve slightly open and all of the gas escaped or maybe did not have the stove connection fully seated? If there is still gas in the canister (sloshes when you shake it) then that is not likely the issue. If not, you could possibly (but unlikely) have two defective stoves?  Self sealing means when you unscrew the stove connection/stove head/burner, the canister will seal the valve - much like a bike tire valve.  Some older style canister stoves would use a puncture method, so once you connected it, you would have to leave it that way until you ran the fuel out.  If staying in the same camp, I will occasionally leave the stove connected and not had any issue with subsequent uses.  I definitely do NOT recommend leaving any stove burner connected to a fuel canister while traveling.  The chances of either stove damage or fuel leakage by the valve getting bumped open are too great.

pd