It doesn't have to work for a mouthpiece and/or reed to be playing OK.
Don't worry about it, only worry if there is something wrong when you play it.
I agree with Pete. However the "pop test" can be a good diagnostic tool if a mouthpiece is difficult to play using a variety of different reeds. I like to look at the tip and rails under magnification when a mouthpiece won't "pop" to see if there is a reason the reed won't close perfectly and create a vacuum. The springiness of the reed, the tip opening, and the length of the lay are all factors that effect a mouthpiece's ability to "pop".
I used the same reed as with the Ed Pillinger. 2 1/2 V16 Vandoren with lots of spring.