I've never had a problem either. Snap pins like this are in use by the thousands on tractors of all horsepower levels. The most common occurance where they come out is on the draft links when a stiff weed or stick happens to push into the ring and flip it open. That would be less likely to happen on the top link pin.
Although most of these pins look alike, there actually are slight differences in the designs of some. In particular, for most pins, the snap lock action is not the same if flipped one way vs. the other. The correct way makes a hard (sometimes finger pinching) snap. The other way may look closed but is not a hard snap. On other designs, the hard snap occurs either way.
I think you probably experienced a fluke occurance. Please reconsider your statement to not use snap ring pins again. The alternative hairpin style clips could also come out, and for sure, you don't want to be putting in a bolt and nut.
JackIL