Just wondering about something? Some craft brews say on the label "Non pasteurized, keep refrigerated. Our beers aren't pasteurized and they sit at room temp for months. Why does boughten need refrigeration?
If I had to guess I'd say you're not getting the caps tight enough. When I get done bottling into plastic, I tighten as much as I can by hand, then take one of those grippers like you open a pickle jar with and give each cap a little more.