I have three pairs of Zymes, bought at different times, and they all did the popper thing, so I find it hard to believe that this is genuinely the case. I think it’s more that as soon as you put any outward pressure on a single popper, as you do when moving around on the bike, the popper simply gives. It’s just not a very clever design.
As I said above, it’s dead easy to fit a second popper yourself alongside the original and it completely sorts out the problem. Those TNF shorts linked above also use a single popper, but they also have belt loops. They remind me a bit of first generation Sugoi Gusto shorts, which isn’t a bad thing.