CW has it, some snaps are called oddly, "Pull Dot" Put the pressure on the dot to open, close it in reverse.
If you look inside of the snap head, there is a spring which is nothing more than spring steel fashioned into a washer-like circle. It should also have a break somewhere and what looks like a sleeve over a small part of the spring. this small sleeve should be opposite of the dot, if not it may effect how it opens and closes.
If the snap is old or well used, this may effect it as well.
If I say bad words, mine seem to snap easier...